# Are C-clamps rated?



## pudgeo2 (Jan 15, 2008)

I was recently talking with a sales rep, who informed me that C-Clamps and Side arms are not rated for overhead use. I can see where this comes from, but I find this hard to believe since C-Clamps have been the standard for ever.


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## soundman (Jan 15, 2008)

Mega clamps are http://www.thelightsource.com/products/1/view 

Malleable Pipe Clamps 500lbs working load <- taken from BMI supply catalog.


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## derekleffew (Jan 15, 2008)

Your rep is correct. Cast iron C-Clamps are not rated, as cast iron, as opposed to forged, is inherently brittle and thus cannot be load rated. We've had this discussion before, particularly in this thread, regarding hanging SeaChangers from side-arms.


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## jmabray (Jan 15, 2008)

Derek is absolutley correct. Cast Iron C-Clamps are not rated. 

But other ones, like the mega clamp or the aluminium clamp from L&E are.


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## cutlunch (Jan 15, 2008)

This maybe a silly question as we don't use these type of clamps in NZ as much. I understand the rating of the clamp but is there a rating on the bolt or this all together? Why I ask is apart from the teeth it seems the tightness of the bolt is what stops the light from falling off the bar if the centre of gravity does not run directly through the center of the clamp.
Here we use Hook clamps the same as Europe.
http://www.blue-room.org.uk/wiki/Hook_Clamps
These have the advantage in that the light will stay on the bar even if the bolt comes loose unless you have the light over the bar. But these are good in schools etc because the bolt normally has a handle not a bolt head. Also the clamp holds to the lights yoke using a bolt with a wing nut. So as long as someone hasn't come along with a spanner and overtightened the wing nut you don't need tools to hang these lights.
Getting back to my inital question, if a bolt is lost out of a C clamp and replaced with one from the hardware store does this derate the C clamp loading capibilty?
I think the last time I used a C clamp was on some old Colortran Fresnels.


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## derekleffew (Jan 15, 2008)

cutlunch, note the LightSource link above. The specs say: 

 Safe Vertical Working Load 600 lb 273 kg

Emphasis on the word "Vertical." The C-Clamp bolt (as opposed to the yoke bolt) takes no weight and is only for holding the clamp in position on the pipe. The yoke bolt on the MegaClamp I have in front of me is a Grade 5.

Not sure why your hangers never caught on here in the US, except for PARbars and pre-Series 300 Vari*Lites. I've often heard them referred to as "G-clamps."


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## Logos (Jan 15, 2008)

The Hook Clamp or G clamp was I believe invented by Strand in the 50's I think there is a wikipedia article.


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## JD (Jan 16, 2008)

Cast C clamps have always given me concern ever since High School (many, many years ago) when I was tightening one and the top just broke off! Wasn't even that tight. Castings are funny things.


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## derekleffew (Jan 17, 2008)

Logos said:


> The Hook Clamp or G clamp was I believe invented by Strand in the 50's I think there is a wikipedia article.


Didn't find anything in wikipedia, but stumbled upon the Strand archive, cited here: 1959 
Strand launch the Hook Clamp and free British theatre from the tyranny of the traditional 2-bolt, 2 nut L Clamp.
Strand Electric's office in Toronto, Canada opens.
The Century Izenour 10 Scene preset is introduced.


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## Les (Jan 17, 2008)

I'm confused. If C-Clamps and sidearms aren't rated for overhead use, where are you supposed to use them? I'm hard pressed to think of any hanging position in a theatre that isn't over someone's head. Is the type of clamp in the picture below what we're talking about?


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## icewolf08 (Jan 17, 2008)

Lester said:


> I'm confused. If C-Clamps and sidearms aren't rated for overhead use, where are you supposed to use them? I'm hard pressed to think of any hanging position in a theatre that isn't over someone's head. Is the type of clamp in the picture below what we're talking about?


Yup, that which you have pictured, is not rated. Take a look at it, you will find that not even the "heavy duty" ETC clamps have an SWL listed on them. As was mentioned it has to do with the fact that they are cast iron, very brittle. This is one of the reasons that it is very bad to over-tighten C-clamps. The angle of force that the bolt applies can bend and weaken the clamp, and eventually, as someone pointed out before, they just fall apart.


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## JD (Jan 17, 2008)

Many things used in theater predate current safety regulations. Heck, theaters used to burn down all the time! Most stuff slowly gets weeded out. Some stuff sticks around... Look around your own home- There is no way in the world the standard Edison light bulb base would ever make it to market if it were introduced today! Most people could get two or three fingers into that one if they tried! Popularity just keeps that one alive.


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## TimMiller (Jan 25, 2008)

When ever i'm buying clamps i look at the side of them and they usually have a working load rated, such as a lot of c clamps have 500 lbs SWL or something like that printed on it, i buy those. If it does not have a load rating printed on it, and this applies from everything from c clamps, to quick links, to shackles, and i also only use graded bolts. They call ungraded bolts "shear bolts" in the farming industry for a reason, when your machine gets in a bind those ungraded bolts are designed to get sheared in half to protect the gears from binding up and being destroyed. And if you have been farming long you learn very quickly how easy it is to pop a shear bolt. Its very scary how easy it is, the bolt will pop before you even hear the engine lug down. Just think of this being a lot of weighht on a light over your head. Also i tell guys think of who you love most sitting under that light, do you feel safe with them sitting there, if not then you should make it where you do feel safe, even if it includes double safety cabling and wrapping a metal chain around it.


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## gafftaper (Jan 26, 2008)

This is a really frightening topic I had never thought about. It's a great reason to preach good safety cable use and to only allow 6" crescent wrenches. I can't believe with all the safety stuff we talk about that one of the most critical pieces of hardware on every stage isn't rated. That's amazing!


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## Sean (Jan 26, 2008)

gafftaper said:


> This is a really frightening topic I had never thought about. It's a great reason to preach good safety cable use and to only allow 6" crescent wrenches.



I cannot disagree more--especially in younger hands.

There are several folks that will disagree, and preach the merits of speed wrenches, etc. But I can't even begin to count the number of times I've been asked "hey, can I borrow your wrench? Mine won't fit".

An 8" wrench will fit all the hardware we deal with on a daily basis. Unless you get a wide-jaw 6" wrench, they often will not fit a scaffold clamp (cheeseborough). And, even if they do many do not have enough strength to tighten down said clamp with a 6" handle.

As to the cast C-clamps. Though I certainly have seen a few broken ones, I've yet to have one break on me (or have it happen on a call I'm on). I would suggest that you look at the clamps each time they're used. If you see any sort of cracks, or if they seems "out of shape", toss them in the trash.

Don't handicap your crew, just teach them how to use the equipment correctly.

--Sean


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## gafftaper (Jan 26, 2008)

To politely disagree with you...
If they need it for a special purpose, there's an 8" wrench in the tool box. But I haven't found a high school girl yet who can't sufficiently tighten a C-clamp with a 6" wrench... and I've taught a lot of them. The problem comes when a guy uses the 8" wrench to tighten it and the girl has the 6" wrench to loosen it.


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## Sean (Jan 26, 2008)

gafftaper said:


> To politely disagree with you...
> If they need it for a special purpose, there's an 8" wrench in the tool box. But I haven't found a high school girl yet who can't sufficiently tighten a C-clamp with a 6" wrench... and I've taught a lot of them. The problem comes when a guy uses the 8" wrench to tighten it and the girl has the 6" wrench to loosen it.



I'm not talking specifically about tightening C-clamp bolts. I'm talking about, for example, the yoke bolts and the nuts on Cheeseboroughs. 

To be fair, I've not spent a lot of time working with HS students (though I do have one as a full-year job shadow right now). I just seems to me making them use 6" wrenches is a short-sighted way to protect equipment. It doesn't actually teach how to USE the tools appropriately.

My $.02. And seriously, no offense intended.

--Sean


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## JD (Jan 26, 2008)

Sean said:


> I've yet to have one break on me (or have it happen on a call I'm on).


The one that broke on me was brand new. It looked fine. Once broken, it was easy to see why- there was a void inside the casting. I would assume (and you know what that spells) that once it has been used awhile, the chance of that happening is very unlikely. Still, I doubt they will ever be magnafluxing C clamps, so it's just something to keep in the back of your mind. I am referring to the old cast iron ones here, not things like mega-clamps which I think have a much better QC. I just remember how surprised I was, and that has stayed with me.


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## gafftaper (Jan 26, 2008)

Sean said:


> I'm not talking specifically about tightening C-clamp bolts. I'm talking about, for example, the yoke bolts and the nuts on Cheeseboroughs.
> To be fair, I've not spent a lot of time working with HS students (though I do have one as a full-year job shadow right now). I just seems to me making them use 6" wrenches is a short-sighted way to protect equipment. It doesn't actually teach how to USE the tools appropriately.
> My $.02. And seriously, no offense intended.
> --Sean



Continuing the debate...

I do have to admit I cheat and use a wide jaw 6" wrench as that is needed occasionally for the yoke bolt. But my feeling with that is you should crank it down tight on the bench and not touch it in the air. Along with that, the last thing you want is someone using a 8" or larger wrench on the tiny pan lock bolt (a.k.a. "Jesus/F-Nut"). 

I certainly see your point that other types of hanging devices may require more than a 6" wrench but for conventional lighting hangs my basic point is you just don't need to tighten the C-clamp down that hard on the pipe. Finger tight plus another half turn or so is plenty. If you are digging into the pipe you've gone too far. I suppose this depends a lot on your inventory, if you use a lot of Cheeseburgers and other large hardware I can see the need for a larger wrench, but in a mostly conventional rig, my vote is 6" only.


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## Sean (Jan 26, 2008)

gafftaper said:


> Continuing the debate...
> I do have to admit I cheat and use a wide jaw 6" wrench as that is needed occasionally for the yoke bolt. But my feeling with that is you should crank it down tight on the bench and not touch it in the air. Along with that, the last thing you want is someone using a 8" or larger wrench on the tiny pan lock bolt (a.k.a. "Jesus/F-Nut").



Hmmm.....

Tightening the yoke bolt is part of both hanging, and often focusing the unit.

Attaching a sidearm tee to a unit is a pretty frequent use of 1/2" hardware. And, it happens on just about every hang.

As for the pan bolt, do you really think it's that much harder to break that bolt with a 6" wrench?

Do you allow students to use power tools? Power saws can do more damage than a regular hand saw can do any day. Just because the capacity/mechanical advantage is there doesn't mean it will be used incorrectly.

--Sean


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## derekleffew (Jan 26, 2008)

I generally get scared when I see guys with more than 8" show up at a call. I've always thought 6" was plenty. Wide-jaw is good too.


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## soundman (Jan 26, 2008)

a 10" wrench will never walk away though as no one will forget about or want to carry it any longer than absolutely necessary.


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## icewolf08 (Jan 26, 2008)

I see gaff's point, and I see Sean's. When I was in college, the requirement for every person on an LX crew was to have an 8" crescent wrench. That is what I carry every day, and that is what I tell new crew people here at PTC to carry. 

Sean has a very valid point in that if you teach someone how to hang a light and you teach that you only need to go finger tight plus another 1/2 turn with a wrench they should be able to handle that weather they bee in HS, college, or a pro. Otherwise you just drill it into the crew until they do get it.


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## gafftaper (Jan 26, 2008)

I love the fact we are having this debate over an insanely minute detail. I think we all agree that a 6" wide mouth will do the basic C-clamp job and I think we all agree about how tight is proper. No it's more a debate about if the 6" is too restricting for other tasks. We all need something better to do with our lives. 


I think it was Ship or Van who a while back told the story of the crusty old T.D. who would take away any wrenches over 6" and cut them off. That'll be me someday.


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## JD (Jan 26, 2008)

The disagreement (in my opinion) seams to have to do with the concept that a larger wrench may lead to over tightening. Finger tighten, then half turn with a wrench would apply the same force no matter what the size is, but then there's human nature to deal with. (The bigger the wrench, the more someone is likely to put the same force at the end of it, which results in greater foot-pounds torque if they don't stop at half a turn.) 

On fact in rigging, construction, and even auto work, is sometime missed by the novice: The tighter you tighten something, the weaker it becomes! The static force has to be subtracted from the maximum working force of the joint. In other words (simplified), if a bolt had a tinsel strength or 2000 pounds, and was tightened to the point where there was 500 pounds of static force, it would now break under a 1500 pound load. 

The compromise has to be in-between what is needed to keep something in position, and the drop in structural integrity. 

I can't place the news article right now, but I remember a walkway collapse that occurred a few years ago that was blamed on over tightening of support bolts. 


I think this debate is a good one because if one person happens across this board who didn't know about the half turn rule-of-thumb, we may have saved someone a lot of grief!


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## Charc (Jan 26, 2008)

JD said:


> The disagreement (in my opinion) seams to have to do with the concept that a larger wrench may lead to over tightening. Finger tighten, then half turn with a wrench would apply the same force no matter what the size is, but then there's human nature to deal with. (The bigger the wrench, the more someone is likely to put the same force at the end of it, which results in greater foot-pounds torque if they don't stop at half a turn.)
> On fact in rigging, construction, and even auto work, is sometime missed by the novice: The tighter you tighten something, the weaker it becomes! The static force has to be subtracted from the maximum working force of the joint. In other words (simplified), if a bolt had a tinsel strength or 2000 pounds, and was tightened to the point where there was 500 pounds of static force, it would now break under a 1500 pound load.
> The compromise has to be in-between what is needed to keep something in position, and the drop in structural integrity.
> I can't place the news article right now, but I remember a walkway collapse that occurred a few years ago that was blamed on over tightening of support bolts.
> I think this debate is a good one because if one person happens across this board who didn't know about the half turn rule-of-thumb, we may have saved someone a lot of grief!



I believe it was the lack of washers, the bolts ripped through the beams, making the walkway collapse.


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## cutlunch (Jan 26, 2008)

charcoaldabs said:


> I believe it was the lack of washers, the bolts ripped through the beams, making the walkway collapse.



I believe you might be talking about the MGM walkway collapse.

There was a documentary on TV here a week ago.
Apparently what had happened was they had welded to beams together to make a box beam. The supporting bolts were placed through the centre of the welds. So apparently eventualy the weight of the walkways distorted the beams around the bolts. The beams finaly broke at the weld and the bolts pulled through dropping the walkway.


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## SerraAva (Jan 26, 2008)

I remember the back in 2003 when the rig at Broadway-Hall collapsed. Was still in high school at the time, but know a few people who were there and have the pictures still. Pretty scary stuff when you thing about it. Didn't know the 'half turn rule' before, but will remember it for future use. Thanks.


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## lightbyfire (Jan 27, 2008)

Not an overtightening incident, but when you said this it made me think of an example given in Structural Design for the Stage, where the 1980 collapse of suspended walkways in a Hyatt Regency. Box beams were partially to blame here too, however it was two stacked walkways that were originally supposed to be supported by one continuous rod, but to save cost the builder used two rods, so instead of both walkways being supported by the ceiling, the lower one was instead hung off the upper one, causing the top walkway to have to support twice its normal load.

I find overtightend C Clamps all the time, I have a technician who insists on using channel locks, and I dont care how careful he is bolts are always overtightened. I myself have bent a number of ETC C clamps by overtightening when overhanging fixutres with scrollers. I have a box of about 20 that are bent.

We have a 24" wrench, but it's a little impractical to carry in your pocket.


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## JD (Jan 27, 2008)

charcoaldabs said:


> I believe it was the lack of washers, the bolts ripped through the beams, making the walkway collapse.



I am thinking the article I read may have been about a different mishap. It was from a few years ago and involved a contractor substituting three screw-rods for a project where the design was for one long one that ran through all three stories. One rod would mean mean only one floor was supported by the threads, but three rods caused the second floor joint to support 2 floors, and the third to support 3 floors or 300% of the design spec. Another factor was the capture bolts which subtracted strength from the support bolts. I will try to find the article.

Just noticed the post above! I think that may be the one. Been a few years!


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## derekleffew (Feb 1, 2008)

Back to topic: Official word from one manufacturer, (guess which one), here.


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## TimMiller (Feb 2, 2008)

So i should quit using ETC c-clamps in place of beam clamps?


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## icewolf08 (Feb 2, 2008)

TimMiller said:


> So i should quit using ETC c-clamps in place of beam clamps?


Probably a good idea.


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## Charc (Feb 2, 2008)

icewolf08 said:


> Probably a good idea.



I don't follow, how would these be interchangeable? Aren't beam-clamps for I-beams, while C-clamps are for pipe?


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## Pie4Weebl (Feb 2, 2008)

TimMiller said:


> So i should quit using ETC c-clamps in place of beam clamps?


You should get rid of your c-clamps (you can mail them to me for disposal) and replace everything in your theatre with uni-strut.


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## gafftapegreenia (Feb 2, 2008)

Pie4Weebl said:


> You should get rid of your c-clamps (you can mail them to me for disposal) and replace everything in your theatre with uni-strut.



Uni-strut...please God anything but that.


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## cutlunch (Feb 2, 2008)

Or you could go European, with the type of clamp I posted erlier and maybe known there as a G clamp. Just imagine not needing a wrench to hang a light. But I suppose all the Americans would feel undressed without the wrench hanging from their belt. LOL.


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## TimMiller (Feb 3, 2008)

i was kidding. I have used c-clamps to hang lights to I-beam. I have a method that works great and is very safe. I hate hanging lights on unistrut, i dont know what unistrut is truely rated for, i have never heard numbers but there is a limit to everything.


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## Charc (Feb 3, 2008)

TimMiller said:


> i was kidding. I have used c-clamps to hang lights to I-beam. I have a method that works great and is very safe. I hate hanging lights on unistrut, i dont know what unistrut is truely rated for, i have never heard numbers but there is a limit to everything.



Which reminds me, is one of my battens supposed to be bent?


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## derekleffew (Feb 3, 2008)

Not unless it's meant to be used for a true cyclorama, aka "wrap cyc." Take a picture, didn't <removed> notice this? If it's minor, it's probably okay, but if it's major
*It COULD pose a serious Safety Hazard!*
*ALL* rigging in *ALL* venues should have a Safety Inspection,
by a Qualified Individual/Company, 
minimally annually.​


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## Charc (Feb 3, 2008)

derekleffew said:


> Not unless it's meant to be used for a true cyclorama, aka "wrap cyc." Take a picture, didn't <removed> notice this? If it's minor, it's probably okay, but if it's major
> *It COULD pose a serious Safety Hazard!*
> *ALL* rigging in *ALL* venues should have a Safety Inspection,
> by a Qualified Individual/Company,
> minimally annually.​



I thought most battens used in theatre are black, but for some reason this looks like aluminum, no that doesn't make sense, I guess it is steel, whatever it is, it's very shiny.

I'd qualify it as a "pretty noticeable bend", however, it's on the pin-rail system, so 1. I won't be flying it in anytime soon to take pictures. 2. The pin-rail gets used like once every four years.

I don't know what the fuss is <removed> installed it.


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## derekleffew (Feb 3, 2008)

charcoaldabs said:


> I thought most battens used in theatre are black, but for some reason this looks like aluminum, no that doesn't make sense, I guess it is steel, whatever it is, it's very shiny.
> 
> I'd qualify it as a "pretty noticeable bend", however, it's on the pin-rail system, so 1. I won't be flying it in anytime soon to take pictures. 2. The pin-rail gets used like once every four years.


Sounds like it's an aluminum-alloy, just like what lighting trusses are made of. See if its O.D. is 50mm OR 1.90". If 50mm (aluminum), probably installed on the pin-rail system to save weight (fewer/lighter sandbags). The only flaw in that logic, particularly for an HS, is when someone, who doesn't know what they are doing, overloads a point on the batten and bends it. *IT SHOULD BE REPLACED BEFORE BEING USED AGAIN. *Bring this to the attention of your Drama Director/Facilities people. Stage Battens should generally be 1.5" BIP, Schedule 80.

And if aluminum, one should not use C-Clamps on it without "Truss Condoms" (Truss Protectors). Wow, almost brought this back on topic...


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## JD (Feb 3, 2008)

TimMiller said:


> I hate hanging lights on unistrut, i dont know what unistrut is truely rated for, i have never heard numbers but there is a limit to everything.



Well there has got to be numbers for it somewhere. It is used extensively in nuclear power plants for hanging everything from wire-ways to core cooling systems. The stuff that goes into these plants goes through some amazing testing and ratings. My only gripe is that it is pretty heavy.


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## Dustincoc (Feb 3, 2008)

gafftaper said:


> This is a really frightening topic I had never thought about. It's a great reason to preach good safety cable use and to only allow 6" crescent wrenches. I can't believe with all the safety stuff we talk about that one of the most critical pieces of hardware on every stage isn't rated. That's amazing!



We don't have any 6" wrenches, the guy in charge of tech says you can't get stuff tight enough with them, only 8" here...


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## gafftapegreenia (Feb 3, 2008)

Ok, we've been over this dozens of time, but if you need an 8" wrench to get it "tight enough", you are either A) too weak for a 6" wrench B) over-tightening the clamp.


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## TimMiller (Feb 4, 2008)

Man you can never get anything too tight. i just use my 24v dewalt impact on every bolt i come across just to make sure its tight. 250ftlbs of torqe insures that its good and tight 


DISCLAMER!!!!!!!!!!!!
I'm completely kidding


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## JD (Feb 4, 2008)

Simple answer, paint the 6 inch wrenches blue, and the 8 inch wrenches pink with flowers. Should fix the problem


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## Les (Feb 4, 2008)

Ok that's funny


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## avkid (Feb 4, 2008)

JD said:


> Simple answer, paint the 6 inch wrenches blue, and the 8 inch wrenches pink with flowers. Should fix the problem


"Real men wear pink."


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## DarSax (Feb 6, 2008)

Sounds like you're going to be losing a lot more 6"ers than 8"ers.


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## gafftaper (Feb 7, 2008)

Dustincoc said:


> We don't have any 6" wrenches, the guy in charge of tech says you can't get stuff tight enough with them, only 8" here...



I'll say it again... finger tight and then give it a half turn with the wrench. It really doesn't need to be any tighter than that... if you've got decent strength in your hands you can do that with a "Mega Combo Wrench"... they are what 3 1/2" long? 

Do all your battens have deep gouges in them?


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## gafftaper (Feb 7, 2008)

TimMiller said:


> Man you can never get anything too tight. i just use my 24v dewalt impact on every bolt i come across just to make sure its tight. 250ftlbs of torqe insures that its good and tight
> DISCLAMER!!!!!!!!!!!!
> I'm completely kidding



Nice one! Tim you are my new hero.


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## xander (Dec 28, 2008)

Well, I wanna add $.02 too!! Personally I like the 8". I am a fairly large person and the 8" feels better in my hand. A 6" just feels small, like a toy. But as far as what other people use, it shouldn't matter. IMO, anything larger than a 8" is just just overkill. It's big and cumbersome and will just get in the way more. If someone showed up to one of my calls with a 12" wrench I would probably make a quick judgment of them. But, as long as they can use the tool properly, I don't care what other people use.

P.S. In the debate between Gafftaper and Sean, I would have to agree with Sean that requiring 6" isn't the right approach. You should be teaching them to tighten the bolt correctly no matter what size wrench they have.


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## church (Dec 29, 2008)

The worst thing posible is people overtightening things and 250 foot pound of torque is definitely in this category. The lug nuts on a typial car wheel only use 95 foot pound, many of the suspension bolts on a car suspension are less than 100 foot pound. In fact the hub nut on the drive axle is usually 145 foot pound or less. All of these fastners have to cope with both dynamic, static and vibration loads which are significantly greater than anything a stage light is likely to experience.

By the way has anyone thought of the safety issue when overtightening fastners and someone slips while attempting to unfasten one of these fastners or worse has to nresort to a cheater pipe on the end of the wrench. Has anyone actually undone a fastner torqued to 250 foot pound - I have and you usually need an air impact gun, an electric impact gun or a 24 inch breaker bar. You will not undo a fastner at this torque level using a six inch, eight inch or ten inch crescent wrench. 

As has been mentioned numerous times above - finger tight plus a quarter or half turn is all that is required.

This thread started out debating the merits of C clamp rating and has explored the important issue of how tight the fastner should be that locks the clamp to the pipe but has got lost somewhere along the way. Remembering that a lot of inexperienced people read this forum we should avoid some of the more esoteric stuff.

Before we get too hung up on rating of c clamps we should also remember that much of what is hung above is not rated - I know no manufacturer provides a rating for yolk on the fixture and none of the fixtures are made from structural steel or 6061 aluminium and none of the bolts on the locking mechanisim are Grade 9. If we are not careful we will identify perceived risks in everything at a level that is unwaranted.


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## derekleffew (Jul 14, 2012)

The after-effects of a 12" c-wrench.


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## Les (Jul 14, 2012)

POP goes the c-clamp!


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## zmb (Jul 15, 2012)

Just like the saw blade showing why staples don't get used with the power saw, there's example for why not to overtighten clamps.


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