Hi, I just put one on a friends rifle.The extra screw's are supplied in case you loose one,which actually is very thoughtful on their part.As for mounting it on the barrel,I put one(1) drop of Blue Loctite on the screw and tightened it up.Be careful not to over tighten the screw or you may round it off,
or you will have a problem! If,you want,you can put some Blue Loctite on the barrel.It will help holding it in place,and,also create a seal.However,I have discovered that the Blue Loctite will only work with a Phosphate barrel,as it will not adhere to a Stainless,or Melonited barrel.And,one more thing
I have to mention.Before you install your gas tube CHECK the INLET hole with a piece of wire! I say this because my friends was not drilled all the way through.I couldn't figure out why the gas tube would only go part way in,after several attempt's.So,instead of getting a bigger hammer like a Moron,
I inserted a piece of wire in the INLET hole and it would not go through.So,I drilled it out,and,was able to install the gas tube like I have done many time's before.Talk about being UPSET,I,was fit too be tied,especially when you factor in the COST of this part! I didn't bother to contact the factory,
because,I figured my friend probably got the one in a million that slipped by QC,And,I didn't want to hear that "since you altered and or modified it" crap.In my mind,I finished the job that they were supposed to do! But,other than that issue,I think that it is well thought out part.Like I said my friend
just happened too get the one that slipped buy.I hope this help's you out.