I have seen people always asking what parts McMaster has for the small parts needed for the AR series of rifles. Here is a list of parts by size,part number, and where they are used on the rifle.

Remember these are sold in bags of 25+ so you will have extras but it saves you money in the long run as you don't have to pay for a single part plus shipping.

I have used all the parts listed without an issue and they are I think the same parts that are bought by companies that do parts kits, that is what I was told anyway by a dealer of small parts anyway.

dust cover C-Clip                                                                    1/8" low clearance black steel

Extractor O-Ring                                                                    1/8 dash 6 O-Ring

bolt catch roll pin                                                     3/32x1/2 mil-spec black phosphate

Trigger Guard Roll pin                                              1/8x5/8  Mil-Spec black phosphate
   
CH Latch,FA plunger,Rear Sight Roll Pin                 1/16x1/4 Mil-spec black phosphate

Ejector roll Pin                                                          1/16x7/16  plain steel

Gas Tube Roll Pin                                                     5/64x5/16  plain steel

FA to Upper Roll Pin                                                  3/32x5/8   plain steel

F&R Swivel and stock roll pin                                     1/8x7/16   plain steel  

Detent spring mod set screw                                      4-40 set screw for detent screw mod to remove stock and rear plate


Coil  Pins  Here is the link to the coil pins and the part numbers and sizes listed below

91598A105     1/16x1/4
91598A632      5/64x5/16
91598A204      3/32x1/2
91598A251      1/8x7/16
91598A253       1/8x5/8

use the above description for the use of pins per sizes

you can leave the plain steel ones uncoated or do a cold blue on them to protect them if you want, I leave them uncoated and just put a film of oil on them and have yet to have an issue with rust.
I linked to plain steel ones as they are stronger then the stainless steel versions but those may be used without an issue.

Hopefully this helps clear up some questions and will slow down the dupes of the same questions being asked a number of times, you can also take the info to your local ace or hardware store to find the parts as well


Mods, Feel free to tack this if you think the info is valid and good enough for it to be.

Thanks

Very nice. Thanks!

Good info, thanks.

Any info like this on springs?

That's what I'm slowly working on next, but I'm trying to cross them and will update when I find them.

The problem is finding the correct compression rate for them as you don't want them too stiff nor too soft.

Thanks!

Sweet!

This needs a tack or flag to keep it out of the archives. 

At one point I had all of the part numbers for the coil pins vs the split roll pins.  I should put that back together.  Maybe somebody will beat me to it.

@AFCarbon15  I can add the coil springs to my list as I have those numbers sitting around as well.

I just didn't add them as I've ran into people that didn't know you can use them as well

Let me know if you want to post it or if I should

Please do.  By all means!

Personally I prefer the coil pins.  There are a few manufacturers using them in their rifles and kits.

Added

You might want to add the 1/8" E-clip part number.  E-clips are easier to install and remove than C-clips, and they stay in place better when you're horsing around with that pesky ejection port door pin.

E-Clip 1/8" E-Clip

Coil spring pins vs slotted tubular spring pins . . .

There are three different types of coil spring pins, light duty, standard duty, and heavy duty.  There is only one type of slotted tubular spring pin.

Of the three types of coil pins none are significantly stronger than the usual slotted spring pins, look at the "breaking strength" column.  The heavy duty coil pins are the only ones that match the strength of the tubular slotted spring pin.

The ones linked are "standard duty" coil pins, those are weaker that the "specified" tubular slotted spring pin.

There are reasons to use coil pins, but none apply in the applications of the AR....

The only reason I can think of is that coil pins are thought of as being easier to install than standard roll pins.  I've never bothered to test that out, as I spent a small amount and bought roll pin starter and driving punches for all the appropriate diameters for an AR.

Oh, there's also the idea that, if they're easier to install, they should be easier to un-install.  I have no interest in that either.

While there's a mind set that "GI parts are always cheap and less robust" than similar commercial parts.  I strongly disagree with that.  Roll pins are inexpensive, but they are very sturdy and were originally specified without regard to what was in the GI inventory.  They are standard parts, available all over the place, so they're used in lots of applications, which is why they were used in the first place.

Rant over...

Did anybody ask VA-gunnut to add this to the "Important Threads" list?
I'd like to be able to refer back to it when I need to.

These make excellent gas key screws.  They are stronger than grade 8.

https://www.mcmaster.com/#92610a190/=10yg49o


ETA: While not shown on McMaster's website, these do have the ribs on the side of the screw head.

I just received a box of these screws and they are very good screws made by CAMCAR. The very next day Ned from M-GUNS came out with > these screws < which are also made by CAMCAR.

Those look pretty good. Only change I would make is using a torx driver instead of the standard allen.

I'd add that the Torx screws in your picture have much better than the "ersatz" knurling Ned Christiansen talks about in his M4 thread.

Just to clarify for those who don't know, the key screws' knurled heads give you someplace to displace material from the key into.  Key screw staking needn't be draconian or Midieval - excessive staking weakens the key.  It only needs to be enough to push key material into the screws so they won't move.

very nice. Love me some McMaster

Very helpful, thank you!

how bout BCG gas key screw?

black alloy steel SHCS #8-32x1/4" ASTM A574, exceeds Gr.8 specs. i would trust bolts sourced from McMaster-Carr
91285A190 pk of 100 $9.02 as of 5/30/17

McMaster-Carr #8-32x1/4" SHCS

I have always hated this type of product description: "These screws are made from an alloy steel that's stronger than Grade 8 steel."

Namely:

All ASTM A574-13 - Standard Specification for Alloy Steel Socket-Head Cap Screws are 180,000 psi minimum, which is the industry standard for alloy steel cap screws under 1/2 inch diameter (and Mil-standard).

SAE, J429 - Mechanical and Material Requirements for externally Threaded Fasteners, requires for Grade 8 only 150,000 psi minimum.

So, by saying your screw are "stronger than Grade 8" does not tell me that they are made to ASTM A574, it just means they are above 150,000 psi, which still can be 29,999 psi weaker that the standard A574 screw.

It seems to me as just a way to sell cheap, off-shore, screws that may, or may-not, meet A574 standards . . .

under the product info tab, the McMaster-Carr screws show hardness of C37, tensile Strength 170,000 psi.  I already did say that they cite ASTM A574.  the Torx screws mentioned above sourced from McMaster-Carr also meet the same specs.

Well, 170,000 psi is not in accordance with ASTM A574 . . .

Neither is HRC 37.

A574 calls for a minimum hardness of HRC 39 and a minimum tensile strength of 180,000 psi, for screws less than 1/2 inch diameter.

Agreed!

Thanks,O P!

While we're on this subject - and not to derail the thread - I see multiple posts noting that Grade 8 is "obsolete" or otherwise deprecated.  Yet parts are still marketed as meeting Grade 8 specs, and Internet Commandos are always spouting "Grade 8 or better" when it comes to gas key screws...

So on the subject of key screws, a) what is the actual MIL-SPEC requirement for these screws, and b) is it in any way beneficial to exceed these requirements, other than being able to say "my key screws are head and shoulders above GI screws"?

The specific screws for the carrier key are not made to any "mil-spec", they are made to a specific Colt drawing, 8448508.  They may have started life as a MS35459-13, but that particular screw was deleted from the specification on 5 April 1962 and the entire specification rendered inactive on 21 Sep 1964.

Current "Mil-spec" cap head screws come under many different specifications, different in material (stainless, alloy, cadmium plated alloy, brass, etc) screw type (UNF, UNC, self locking, locking insert) and head type (drilled, undrilled). All of them are either cancelled or inactive.

The primary catch-all specifications currently used by the military are (which incidentally are the same as screws made to ASME B18.3 and ASTM A574):

- Aerospace Industries Association - National Aerospace Standards, NAS1351, Screws, Cap, Socket Head, Undrilled and Drilled, Plain and Self-locking, Alloy Steel and Corrosion-resistant Steel and Heat-Resisting Steel, UNRF-2A

- Aerospace Industries Association - National Aerospace Standards, NAS1352, Screws, Cap, Socket Head, Undrilled and Drilled, Plain and Self-locking, Alloy Steel and Corrosion-resistant Steel and Heat-Resisting Steel, UNRC-2A

There are other specifications for special threads, unique materials, and other non-standard types under AIA/NAS.

"Grade 8" bolts are not obsolete, they just refer to a different type of fastener, those made to SAE J429, Mechanical and Material Requirements for Externally Threaded Fasteners, this specification includes screws, bolts U-bolts, studs and screw/washer assemblies.  Bolts made to J429 are usually found in automotive and architectural structures.  I do not denigrate grade 8 bolts, it is just a different animal.

To be honest, the actual screws specified (8448508) are required to withstand a 130,000 psi proof load, which would equate to 160,000 to 170,000 psi tensile strength. So, AIA/NAS NAS1352, or ASTM A574 marginally stronger (2520 pounds at yield versus 2380 pounds at yield).  And, the 8448508 screw is HRC 36 to 47, the AIA/NAS NAS1352 and ASTM A574 are HRC 39 to 45, a slightly narrower range, and who knows, maybe those extra two points of hardness make some screws more brittle (I doubt it).

I would say any ASTM A574 screw with a really pretty knurled head will work fine.  (Note: all of these specification state "plain or knurled heads optional", in this case the knurling is more important than the strength.)

IIRC, McMaster-Carr carries a roll pin that is 1/64 smaller than the spec for the trigger guard. Since those are notoriously tight and so many damage their lowers trying to get them installed, I wondered if anyone had ever tried that size.

The specified pin is nominally 0.125 diameter, but the actual pin diameters are 0.131 to 0.135 inch for slotted spring pins and 0.131 to 0.138 for coiled pins.

The print calls for a 0.127 +.002 inch hole for the trigger guard, I'll bet most of the problems come from manufacturers drilling standard 1/8 inch (0.1250) holes, which is a standard drill size, instead of .127" holes, which is right in between two standard sizes, 1/8 inch and a #30 drill (0.1285").

A 1/8 inch drilled hole will definitely be tight, if you get a maximum diameter pin.

Any pin 1/64 inch smaller than a 1/8 nominal pin would just fall out, it would only be 0.119 inch diameter.

I'd bet a whole quarter that the "let's go with 0.125 since it's a common and standard drill size" is spot on with some lower makers.  I've run into some noticeable variation in those holes when installing the "Helicoil trigger guard mod".

It may be my search-fu being weak, but I'm not finding any knurled-head 8-32 1/4" ASTM screws on McMaster's site...

Compare the difference in nominal and actual diameters for the .125 pin, then apply that to the .119 pin

A nominal 1/8 inch roll pin is between 0.131 and 0.135, 0.006 to 0.010 inch larger than nominal.

1/8 - 1/64 = 7/64

7/64 is .109

Bump that up 0.010 inch you get .119 inch, 0.005 inch under the .125 inch hole.  Even the 0.013 inch increase given to the coiled pins would put a 7/64 nominal pin at 0.122, still under-sized.  

You want a minimum of 0.002 inch interference to keep a spring pin locked in a hole, 0.004 to 0.005 inch interference is optimum.  

The knurling is optional on all currently standardized cap screws, so the picture will not necessarily be indicative of what you get.

Unless you order several thousand, and get to write the purchase order to require knurled heads, you have to take your chances.  (Although, in my experience, the knurled head is by far the more common variety.)

Oh, and when drills wear, they get smaller in diameter, but the holes tend to get bigger . . .

And here's what McMaster Carr said when I asked if a particular screw (8-32 x 1/4") was knurled:
They did say they'd let me return them for a refund if they didn't "work for your application."