Torque cycles for fasteners?

[mark5pt56]

As there are many variables involved, is there any industry recommended number of times a fastener can be torqued?

This stems from the need to remove the barrel clamp screws on a Sig MPX for access to the gas piston, new spec is 60 inch pounds on the two bolts.

More of a curiosity, yeah I know you can buy new ones.

While not an AR15, there are fasteners on these guns(accessories)

[georgeib]

This is a great question. My understanding of this is that as long as the fastener (bolt) hasn't been torqued beyond it's yield point, it's safe to reuse. However, I've never read anything about the number of cycles a bolt can take below it's yield point. Excluding single use torque to yield fasteners, or course. I'm curious what the experts, such a lysander, have to say.

[lysander]

As there are many variables involved, is there any industry recommended number of times a fastener can be torqued?

If it is critical - once.

If it is not critical - until it is buggered up and looks bad.

TTY fasteners are a different kettle of fish altogether.

[mark5pt56]

I figured as much, maybe if I remember 5 years from now I can say. Then we all can argue as to what's critical. Thanks Lysander.

[the AR-15 Junkie]

delete

[Clint]

What are they threaded into?

Hopefully some kind of steel nut plate or at least a heli-coil, rather than just the other side of the aluminum receiver.

[ndmiller]

If it is critical - once.

If it is not critical - until it is buggered up and looks bad.

This sounds right on.

My experience with fasteners on motorcycles and manufacturer specs mimic this as most fasteners are reusable, but some brake component fasteners require replacement according to spec. I think it's about the stretch applied to these critical fasteners to ensure they reach their holding spec when tightened, but I'm sure someone smarter can comment. That stretch reduces future "holding" power requiring the replacement spec what what I assumed. All these fasteners are only touched during brake rotor/system replacement after many thousand of miles. But at 2-4 per bolt some riders still reuse anyway.

I've never looked or s there no replacement spec on castle nut or barrel nut or receiver extension? Or just a replacement based on inspection and condition?

[P2Vaircrewman]

As long as the fastener is not stressed beyond the yield point ( point at which it will not return to it manufactured length) the cycles are theoretically limitless. A high pressure gas cylinder such as a scuba tank must be tested every 5 years. The test involves pressuring the cylinder to a pressure just under the yield point of the steel or aluminum it is made from. How much it stretches is measured and and it must return to its original size when the pressure is removed, simple explanation.

Just use the recommended torque for the size and material the screw is made of and go on your merry way. Screws break or strip when tightened beyond the tensile strength of the material.. When I was building racing engines I sometimes used a stretch gauge rather than a torque wrench to tighten connecting rod bolts. It is a better way but cannot be used in all situations.

[GH41]

GH41--I removed your comment--don't be a pest

[mark5pt56]

There's a steel plate that the two screws go into and are removed for the barrel to come out. All makes sense, I'll pick up a couple spares anyhow.

A pic
https://inleadwetrust.com/product/mp...et-barrel-nut/