Allen Hex Key Torque Approximation

[Brians356]

I'm installing a red dot optic on a pistol slide. A spec I have gleaned indirectly (in another forum) from the manufacturer is to apply ~15 in/lb torque to the mounting screws. This is not a critical spec, and not mentioned in the optic's little installation guide. But, I wish to get somewhere in the ballpark.

Not having a torque driver to hand, I decided to poke around online. Blue Devil makes hex keys and provides various dimensions and specs for them. The key I am using is a 3/32" standard 'L' key. Blue devil lists the "Torque Rating" for one as 33 in/lb. They explain that spec as:

Torque Rating ... torque values which keys transmit when the short arm is inserted in a socket and the long arm is deflected or bent through an angle of 25-30° by the application of force near the end of the long arm.

Cutting that in half (for about half the torque) yields ~15 degrees of deflection. The key's long arm measures 2.35", and that translates to roughly 5/8" deflection at the end, easy enough to draw to scale and visualize.

My question: In practice, would one tighten the screw until it's snug (and no longer visibly turning) then start eyeballing the arm's deflection from there?
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[rijndael]

You may find it interesting that Badger Ord has a tightening instructions for when no torque wrench is available:

For the side bolt: "If no torque wrench is available, using a 1/2" wrench, turn the nut 90° after finger tight. "

For the ring cap: "holding the short end of the T-15 wrench tighten about as tight as you can get it."

https://www.badgerordnance.com/media/binaryanvil/media_library/Mounting_rings_and_bases_2017.pdf

 

[LVLAaron]

Snug but don't strip it out. You'll be able to feel it. Use some retaining compound (Loctite 620)

Torque Tools | Fix It Sticks

Say goodbye to stripped screws and fasteners. Compact and precise, Fix It Sticks Torque Tools make over-tightening or over-loosening nearly impossible.

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[Brians356]

If memory serves, a lever 2.35" long requires 6.4 lbs force to match the torque of 15 lbs on a 1" lever. So it's akin to lifting a 6.5 lb rifle by the trigger guard with the index finger.
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[Dusty Stevens]

Why dont you just get like a wheeler torque wrench kit? Youll need it for everything on guns and it has the bits

 

[Brians356]

Why dont you just get like a wheeler torque wrench kit? Youll need it for everything on guns and it has the bits

That's a viable approach, and one already considered, but it fails a comprehensive cost/benefit analysis here. The bar is high since, at my time of life and level of accumulation, there's a shift well underway from acquisition mode to liquidation mode. Only a truly critical need rates a waiver.
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[muleystalker]

As stated above put the long end of the L wrench in the socket screw and use the short end to tighten, stop just as the wrench starts to deflect.

 

[Brians356]

As stated above put the long end of the L wrench in the socket screw and use the short end to tighten, stop just as the wrench starts to deflect.

With the short end only 3/4" long, that's gonna bite. Not sure my fingers are that fit!
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[LVLAaron]

With the short end only 3/4" long, that's gonna bite. Not sure my fingers are that fit!
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Perhaps you should consider a different gun



I kid I kid.

 

[muleystalker]

With the short end only 3/4" long, that's gonna bite. Not sure my fingers are that fit!
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Thats kind of how they are meant to be used, the amount of force you can get on the short end is all the torque the screw will take without stripping out the inside of the head. Put a little blue lock tight on and tighten like above and you will be fine.

 

[Riesel]

I found a pretty decent one on Amazon that I carry in my Range box. Compared as Identical to my Wheeler Fat Wrench for torque

 

[Alex Wheeler]

Tighten it until the threads strip then back it off a 1/4 turn Honestly thats what your trying to do. The long t handles from Bondhus work well because they twist and prevent you from over doing it on small stuff. I recommend them if you dont have a good "feel" for it.

 

[6MMsteve]

snug, kinda tight, pretty snug, cheater, hammer, 50 ton crane and strap, excavator tight, 25 ft 4 inch tube 4 people swingin tight, tighten then weld, mule & harness tight

 

[3Ackleys]

I have the fat wrench and just got the fat sticks, individual preset torque wrench set. I like them better than the adjustable wrench.

F.A.T. Stix™ Preset Torque Wrench Set | Wheeler

F.A.T. Stix™ Preset Torque Wrench Set

www.wheelertools.com

 

[Brians356]

Update: I used fingers on the short arm of the 'L' key, pretty much as much torque as I could muster. I felt the shaft twist slightly. In removing the Springfield OSP cover plate, I noted it took about that much pressure to bust them loose. The optic's included screws already had blue compound on them so I didn't add any Loctite. Of course I'll monitor the screws closely for a while, just in case.

I'm pleased to note the red dot seems aligned with the open sights, but until I check some targets I won't know for sure how it co-witnesses.
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