I was wondering if anybody knows what the McMaster Carr part number is for the Aero Precision threaded bolt catch pin/set screw. I know that it is a 6-32 thread, but I am not able to find the same screw on the McMaster Carr site.

https://www.aeroprecisionusa.com/m4e1-threaded-lower-catch-pin

I have been toying with the idea of buying a 6" 6-32 pull through tap and a 6" #35 drill bit so I can drill and tap some of my receivers that use a roll pin instead of a set screw. My friend and I like to build rifles and sometimes split fastener orders from McMaster-Carr as they are usually dirt cheap for parts that are sold by online stores for a massive markup.

As an example, these set screws are sold for $1.99 a pair here and you can buy a box of 100 of them from McMaster-Carr for $20. Since these are one time use screws, this is a no brainer to me.  I am looking to do the same thing with these set screws.

Not something M-C would have, it's a specialty part only made for ARs.

You could buy a longer set screw, and turn down the end, if you are good at machining miniature parts,
or just stop being so cheap, and buy the ones already made by Sooo many people.

While I don't agree with his sentiment, I believe his conclusion is correct; there isn't anything on McMaster and it would be cost prohibitive to do these one at a time...

Just exactly how often do you people remove the bolt catch?  Carefully put the spring pin in with tape and a brass punch, and leave it there.

I have never understood the need to make things more complicated just because we can.

From my limited searching it appears these types of screws may be referred to as "full dog point set screws" or "extra long extended tip set screws" but I haven't found any with the tip as long as what Aero Precision sells.

images from search "full dog point set screw"

On McMaster Carr, either of the 6-32 versions, 3/16" or 1/4", the longest tip is 0.076" and the length difference is in the threaded portion.

McMaster Carr extra long extended tip set screws

Somebody makes them and it is not Aero.

I would love a box of them for just incase.

I bought about a hundred of 'em from CDNN, when they were selling off the DPMS leftovers. They were like $2 each, with shipping. Most places want $5 or so for these things. And no, I ain't gettin' off any. Probably used 30 already between my friends and myself.

FWIW, bolt catch set-screw, $2.49 at Midway, their AR-Stoner house brand

Quentin Defense has them also.

A dog point setscrew only has a turned point about 0.08" long.

There is a half-dog point that is about 0.03" long.

The set screw used by all the bolt stops is a special screw

You could contact this guy on Gunbroker, and ask about a volume purchase.
Aero Bolt Catch Screw