Found this out the hard way with a T-1 - when going from from a LaRue mount and (yet again) re-using the screws to attach it to the stock, no elevation mount. Still need to get it to a machinist.
McMaster doesn't list country of origin on the site, generally.
I just looked at the last order I have from them, still sitting on my work bench. Origin is marked on the boxes. SAE sizes are from US, except for a bag of washers that's "CN" (probably not Canada), and metric sizes are from TW. The coating on the TW screws is cleaner and more uniform, generally.
So it appears McMaster sources hardware from wherever seems best to them, just like Fabory or any other quality distributor.
H-K makes me happy, but I don't worry about a YFS mark.
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Not another dime.
I don't care much about country of origin as long as I can get a cert and the country is on the DFARS list.
McMaster Carr is your friend. You can buy a box of high strength alloy or SST screws of your liking for around $20 a box of 25. Thats 12 battery changes. Re-using teeny screws that are torqued and beat on by a reciprocating slide isn't saving you that much $$.
DP Pro just came loose on a Shadow 2 slide, direct milled by Primary. Screw broke.
Likes pretty much everything in every caliber.
Maybe you need one of these:
https://www.amazon.com/Alden-4507P-G.../dp/B000Q60UOO
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Not another dime.