I have used a few of these - Matrix Arms AR-15 Victor M-LOK Handguard

I've used these for rifle and pcc builds and they all work great. Barrel nut is standard flats (1-1/16 I think) so you can use an adjustable if you dont have a box end or crows foot. I have had no issues. I like the 3 set screws. Clearance is good for most gas blocks but it wont fit a suplerative arms adj gas block which is not low profile. Havent had any issues with fit up and mating to the upper of the rails. I have these handgaurds on very large calibers and pistol caliber uppers. A great value.