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Thread: Grip screw torque value: creating a max specification?

  1. #1
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    Grip screw torque value: creating a max specification?

    Hey there everyone,

    I was installing a new MIAD grip onto one of my BCM lowers the other day (thanks Grant!), and it got insanely tight only half way through the installation process. It eventually froze, and I feared that I cross-threaded the threads. After removing everything, the threads turned out to be fine and it was just Magpul's cement-like compound pre-applied to the threads that jammed everything up (holy crap, Magpul, that stuff needs to go). I removed their compound, applied some blue Loctite, installed the grip until the screw was snug against the plastic, and went a quarter turn further.

    This got me thinking that there's got to be a better, more precise way to do this to ensure one doesn't strip the threads. Turns out there isn't a spec that I could find other than a mention of 35 in-lb on here in in 2006. Knowing that there are general specs out there for all materials and threads, I started searching to see what I could find. Found these sources:

    http://hydraulicspneumatics.tpub.com...338-12P_67.htm
    http://yetmans.mb.ca/kohler/page3/page3.html
    www.ligo.caltech.edu/docs/T/T970244-00.pdf

    It looks like the maximum torque value for 1/4-28 threads at a minimum of 0.5" depth is between 55 in-lbs. and 120 in-lbs for aluminum. Obviously it depends on the type of aluminum, but overall, it seems like you don't want to exceed 55 in-lbs. For those of you with more experience than I do, does that sound right?

    This also leads me to think, how the hell do people strip their grip screw threads in the lower!? 55 in-lbs with a flathead seems like an absolutely insane amount of torque. I was scared I would strip my threads at snug+a quarter turn, but man, that's a lot. I can't even see hitting that without socketing a wrench to the driver. Are people putting their lower in a vice and putting a gorilla grip on their screw driver?

    ...but I don't have as much experience as you guys. What do you think? Don't exceed 55 in-lbs on your grip screw? And what would that "feel like"?
    Last edited by DreadPirateMoyer; 09-22-13 at 15:02.

  2. #2
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    There is no torque value. Often. times the resistance is due to the large amount of thread locker on the screw. All you need to do is snug the screw. Of course using the star lock washer helps.



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    Quote Originally Posted by DreadPirateMoyer View Post
    After removing everything, the threads turned out to be fine and it was just Magpul's cement-like compound pre-applied to the threads that jammed everything up (holy crap, Magpul, that stuff needs to go).
    I had the exact same issue installing the MOE AK grip on my Arsenal. I thought I'd buggered things up good when I stripped the flathead trying to tighten it down and there was still significant wiggle on the grip. I miracled the screw back out with some channel locks and the threads were fine. Replaced it with a hex-head stainless screw from the hardware store and everything went together normally.

    Side question: for a situation like this, would a lock washer be sufficient to secure a grip screw, or should we stick with blue loc-tite?
    Last edited by CrazyFingers; 09-22-13 at 15:30.

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    The compound on the Magpul screw is not an anaerobic thread locker like Loctite but a variant of Vibra-Tite which isn't permanent. It's a resin compound which allows it to be adjustable and reusable. This isn't the case with Loctite. Using Loctite on the grip screw is bad idea in every circumstance.

    A torque value can't be accurately applied due to compression of the plastic between the screw head/washer and tang on the lower receiver. Hand tight is all you need. That being said, the Magpul screw is a cheap piece of shit. There is a reason the mil-spec variant is a fillister head and uses a lock washer...

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    One problem with that hole is that a lot of shops run a tap in the hole, but do not follow with a bottoming tap... so you get a thread hole that tapers as it gets deeper - most of the time not a big deal, but it can compound a problem.

    I always run a hand tap through the hole (all the way through) before building a new lower... just a thought.
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    Quote Originally Posted by K.L. Davis View Post
    One problem with that hole is that a lot of shops run a tap in the hole, but do not follow with a bottoming tap... so you get a thread hole that tapers as it gets deeper - most of the time not a big deal, but it can compound a problem.

    I always run a hand tap through the hole (all the way through) before building a new lower... just a thought.
    I'm not sure I understand the value in this operation. Chasing the threads is going to remove the anodizing. Cleaning compounds or water may lead to a bit of corrosion. The first six threads on the screw do all of the work. That's about 0.215 of an inch. If screw length is an issue, wouldn't it be easier to customize the screw?

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    Just get rid of the blue smeg they use on the screw & you should have no problems.

    I haven't had anyone complain with the dozens of Magpul grips I have installed.
    "Freedom is never more than one generation away from extinction. We didn't pass it on to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same, or one day we will spend our sunset years telling our children and our children's children what it was once like in the United States where men were free." President Ronald Regan

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    This is precisely why I carry a 1/4-28 die in my armorers kit. I use it to take off the gunk Magpul uses and install using 222MS Loctite.

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    Quote Originally Posted by MK18Pilot View Post
    I'm not sure I understand the value in this operation. Chasing the threads is going to remove the anodizing. Cleaning compounds or water may lead to a bit of corrosion. The first six threads on the screw do all of the work. That's about 0.215 of an inch. If screw length is an issue, wouldn't it be easier to customize the screw?
    Good question... keep in mind that often I will start with a lower in the white, especially when there is custom deep laser engraving. But your concerns are valid; I have a very worn finish tap on a t-handle that I run through the hole on lowers... it is not going to cut anodizing but it may clean up some junk (just like when you run a pin drill into the detent spring holes and clean out chips and bead blasting media on some lowers)... I just like to check those things before I put something together.

    Honestly, modifying the screw would work - but I can't help but wonder why I would have to modify parts if the lower was in spec?

    The "six threads" thing is a rule of thumb... keep in mind that you can discount the first thread or two in the hole as they are usually malformed or out of class requirement - also, most people that I know recommend going fastener diameter times 1.5 when you are screwing steel into aluminum... 10 threads is a safer bet.
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  10. #10
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    I may be over cautious but some loctite products including 222MS don't get along well with some plastics. GH

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