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Posted: 5/25/2006 2:53:52 PM EDT
I was just looking over the post about correctly staking bolt carrier key screws. I noticed that the screws had 2 different size allen key recesses. Where can I get the allen head screws for the bolt carrier key that uses the smaller allen key? I like the idea of having the extra metal in the screw head. I know Colt uses them, but where in heavens name can you find them? TIA. 
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Uh, the drive size was increased in 1960, to reduce stripping of the heads & wrenches. The "extra metal" in the head is not a positive thing. If you find the pre-1960 head pattern, it is probably an import screw. Or some really old stock. The screw size is 8-32 x 1/4 . Lem |
Gee, that's funny. The Colt carriers at my house, all 6 of them, all made between 1965 and 1985, all have the smaller sized slot. (Mutters to himself) "Lord save us from experts". |
Thanks j3. That is the kinda info I was looking for. I had checked Brownell's and they were back ordered. I will have to check with Specialized Armament.  |
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Well, shamalamma five thousand posts don't make you an expert either. Try this LINK, specifically page 5 of the pdf. Right from the screw manufacturers own web site. The STANDARD 8-32 head size is 9/64" Period. I suppose colt could have 1936 pattern screws run someplace, but there is NO reason to use the smaller hex. It is easier to strip both the driver & the head. In my experience, the new stock that shows up with the smaller hex came from some third world place like India. AR-10 Man, you have a MUCH better chance of getting to the 50 inch-pound figure Armalite recomends if you use the larger hex size. Lem |
| Smaller hex means more metal attaching the head to the screw. The screw takes little torque to tighten it. If a manufacturer specs a non standard screw I would think they most likely did it for a technical reason since the cost might often be more than the off the shelf one. |
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J3: Given that the original design dates to the early 1960's this could be a specification that was never rewritten. In 1970 I still found plenty of 1936 pattern screws on the shelf. Colt's purchasing department may in fact be going to great lengths to buy obsolete screws. The added material does not increase the strength, it just makes the driver smaller. Tap a hole into a piece of steel, and torque an 8-32 capscrew against a washer until it breaks. It will break at the first thread under the head, regardless of the hex size. 50 to 60 inch pounds is a lot for an 8-32 screw. You should specify quality screws from a known supplier. If you open the box to find a label that says: "contents may haven been made in the following countries..." You can take your own chances. I have installed thousands of allen screws in my career, and breaking one off in a $20,000 die is a real bitch. Every time I have broken a screw, the box had those words on it someplace. Stay with Unbrako, Camcar, or Allen if you can. Lem |
Never claimed to be an expert. Just that Colt was using the smaller slot long after your "expert" opinion said they were. You want to claim expertise on screws, feel free. I guess everyone needs at least one thing to feel good about. I will add that after 33 years of Colt AR15 ownership, I have never had a carrier key screw break. But then, I don't mess with them. They're there, they're staked, and I leave them alone.
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In my most recent order from Bushmaster I received a (carrier key+screws). The screws were of the old style 1/8" Hex. I thought this was strange so I E-mailed Bushmaster about it. The Tech at BM said that they no longer use the 9/64" Hex and now only use the 1/8" Hex screws. They also said that the 1/8" Hex screws can be torqued up tighter because they are stronger. I don't know if what they said is true, but there it is. Also, I wouldn't think that Bushmaster would use parts from India, but you never know. 
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Well there ya have it! More mud in the water.  Lem that link had some great info, and it makes me feel better about the brand name hex screws. I still feel and have read some where that the smaller drive screws are stronger. The article in the link leads one to believe that brand name hex screws are plenty strong enough. I guess ya takes yer pick and just run with it. Maybe I will just get some 8-32 x 1/4 torx screws. ETA: found the info i was looking for. It was for a set of replacement scope ring and base screws. It said the smaller hex drive made for a stronger screw. |
Glad I could help.
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If you really want a strong screw, find one with the Torx head. The allen head is one of the worst inventions of all time when it comes to torquing. Unless the hex key and the screw are an exact fit, you have very poor engagement of the driver, and can easily strip the head of the screw. I am sure that you could find them on-line somewhere (Textron is the primary manufacturer of Torx here in the US), and it would be far superior to even a 1/8 drive allen screw. I am sure they are probably grade 8 as well, which would reduce the chance of breaking one, but can create problems with getting them tightened correctly (but that is what staking them is for). 5Shot |
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