Ok, quick share in case it might help anyone.

Purchased a 15" UTG SS M-Lol rail for a new build... I know, it isn't BCM or DD, etc.

I found I just liked it, and grabbed one.

Initially I was impressed with it once installed.  However, looking closer, the barrel was not centered, nor was it holding tight to upper receiver.

Lesson learned, ok, ok.

So, I did a little research on here, found an archived post on the 9" UTG SS Keymod version from a few years back. References McMaster Carr screws as a possible solution and a link.

Ordered them, installed them. The screws supplied by UTG are soft, strip easily and are too long. The supplied screws were actually able to touch the barrel through the barrel nut, creating a loose uneven pivot point.  Once I used the new screws, the rail is straight, true, and solid.

UTG never got back to my email about my issue, so ordering 7 dollars worth of screws fixed it. Wanted to share in case others run into this. A solid and reasonable product shouldn't be "screwed" by a 10 cent fastener.

Thanks. Fastener info below. Can confirm works with UTG SS Pro M-Lok 15" rail.

McMaster Carr website...
92137A301Hex Drive Flanged Rounded Head Screws, Alloy Steel, M4 x 0.7 mm Thread, 6mm Long, packs of 25