Question for the Armorers; What is your source for quality American made gas key screws? I hesitate to say mil-spec because if there is a mil-spec gas key screw it seem unobtainable.

I use Unbrako brand.

Note; I’m not an armorer. Just a machinist that uses lots of nuts and bolts. We’ve always used Unbrako. You can buy a box of 100 at granger. Not sure where to buy singles unless you order from a vendor such at midway, primary arms, or WOA


$1.50 Here

OCKS

Forward Controls Design OCKS

https://www.forwardcontrolsdesign.com/OCKS_p_149.html

OCKS from the source.

Michiguns Ltd.

Where can you get the carrier key screws with the 1/8 socket head?

They show as OOS, but Brownells lists the Colt screws at $5 each. (They also have a house-branded version at $2, but also OOS.  Not sure about 1/8 vs 5/64 drive on these.)

Is that you need some and can’t find any?
Or don’t want to pay expensive shipping for $2 in parts.
Either way I can mail you 2 if you’d like
PM my your address and I’ll mail them out Monday.

McMaster.

https://www.mscdirect.com/product/details/01844968
First ones I got were US made Brighton Best but they were bought out by YFS and the last box were YFS marked.  Still met the same ASTM spec just Taiwan made. The only other US made ones I have found by the box the knurling on the screw looked faint in the picture and only covered a short length on the side. If other companies in the US make them I have not found them in their catalogs or online for sale. If you do a search they are called 1936 series socket screws instead of 1960.

The first two posts are where you need to be looking.

There appears to be differences in the mil. drawing screw and a 1936 or 1960 series standard socket screw. The knurling requirement, the finish, the type steel is spec'd instead of all of types the ASTM allows to be used, at least one dimension appears to be slightly different,  and the thread class appear to be different. It is not just the socket size being different than a 1960 series screw.

Can you provide a link to the mil drawing?

No but if you are looking for more information the screws are discussed on the other side in the AR general section on page three of the current milspec roll pin thread.
If I had the nerve and money I would try ordering a few 8448508 screws off armypropery.com to see what I got.

Quite true.

ASTM A574-13 and NAS 1352 standards allows for steels with the following composition:

Carbon - 0.31%
Phosphorus - 0.035%
Sulfur - 0.040% max
one or more of the following to ensure strength requirements are met - chromium, nickel, molybdenum, or vanadium (That covers a lot of steel alloys.)

The mechanical requirements are:

Tensile strength - 180 ksi
Proof load - 140 ksi
Hardness (Rc) - 39-45
Yield at 2% - 153 ksi
Elongation - 10% min (Most 41XX and 43XX series steel this is 15% to 20%)
Reduction in area - 35% min (Most 41XX and 43XX series steel this is 40% to 50%)

DWG 8448508 calls for AISI 4037 heat treated and tempered to 15N 78.5 to 83 (HRc 36 to 45).  At this hardness 4037 will have the same ultimate and yield strength, but the elongation will be only 5% and the reduction in area of 36%

So, what the difference? It's all steel with the same yield strength, right?

Well, the strength and hardness are the same but the other properties have a bearing on the behavior of the screws and explain why Armalite/Colt's was so specific in material choice. The elongation at break is 5%, and 36% reduction in area for 4037, the other alloys have values in the 15% to 20% elongation and 40% to 50% reduction in area. This means that 4037 is a very "stiff" alloy, in takes a lot of force to stretch the material a small amount

Also, the required torque on the 8448508 screws is 58 in-lbs, which means the clamping force is between 1,793 and 2,080 lbs. Clamping force is the result of the steel of the bolt stretching like a rubber band and holding tension.

The proof load for 8-32 UNC ASTM A574 screws is 1,960 lbs.  Proof load means the bolt stretch at this load remains inside the elastic region of the stress-strain curve.  Loads above the proof load can result in permanent bolt stretch and loss of torque and clamping load.  So, some ASTM A574 screws can stretch under this torque.  4037 screws, being stiffer, do not stretch as much and therefore retain their clamping load.  This is why BCM and Colt's use the 4037 screw.

(You can mitigate the bolt elongation problem by simply reducing the torque to about 50 - 55 in-lbs and making sure the screws are installed dry.  You still maintain a 1,500-1,700 lbs of clamp.)

Also, there is that one dimensional difference, ASTM A574 and NASM1352 screws specify a 9/64" (0.140") key and the DWG 8448508 screws specify a 1/8" (0.125") key.  Since the head diameter is the same, the drawing screw has a thicker web.

Does it matter?  I don't know, that's up to you.  Personally, I can live with the minor differences, but just be aware that there are differences.

Since this screw is an industry standard for Colt, BCM, Microbest, why is it unavailable?

The 8448508 screw is not industry standard.

There are other minor differences, the diameter of the Colt head is held to +/- 0.004 (vs +/- 0.007), and the type, quality and depth of the  knurl is more specifically defined.

These are essentially bespoke screws, You contact a screw manufacturer and tell him to make some screws to this drawings, and a few months later you get a million screws, or whatever his minimum run is, for about $0.05 each

Specialized Armament sells them,$5/2.

Is 8448508 the Colt and BCM Screw?

It is the screw called out in the data package.

For clarity, standard cap head Allen socket screws can be either knurled or not, unless specified in the order to the manufacturer.  The data package calls for a specific knurling pitch and depth.  This goes beyond industry standards by quite a bit, and appears to be specifically to provide “bite” for staking the key into.

So you can get an 8-32, 1/4” long, fully threaded Allen socket cap screw from many vendors.  But you aren’t going to find any bulk vendors that guarantee every lot of their screws will be knurled, let alone knurled in the quite aggressive manner called for.  This means those generic screws may or may not lend themselves to staking.

Michiguns’ Optimized Carrier Key Screws feature specially manufactured, deep knurling that extends the whole length of the cap, with an added 12 splines to provide even more space to stake into.  Read their write-up about why they go to the trouble of making special screws.  (You have to select the OCKS product to get the product window to open.)

Finally, if plain old 8-32, 1/4” long, fully threaded, Allen socket cap screws would do the job, penny-pinching Uncle Sam would have specified them, even if Colt originally called for fancier screws.

And nobody knows where these screws come from....

Which screws? I think the special order ones from michiguns are special order and design. Pics online appear to show Camcar markings on them. Camcar hard to tell who owns it. The other Gov. ones probably are bid out to screw manufacturers by whoever has legal access to the design when a bid from someone requesting a quantity of them comes out.

Contact some screw manufacturers for quotes.

Be prepared to buy in bulk.