If it is hard to attach to the rifle - do this:
Screw in the screw WITHOUT the grip and then remove it so some of the threadlock material gets worn off.
Heat oven to 170 degrees F, place grip in oven for 10-15 minutes, remove from oven, then slide the grip onto the rifle. Be sure the spring is in the hole in the receiver and then slide it into the grip hole so it does not bind while doing this.
Then screw in tightly the supplied screw. Function check to make sure safety/fire switch works.
I got this from one of the AR-15 forums. It worked for me! YMMV.
My theory is that when it heats up, the grip expands to the correct width. When it cools down, it will be really stuck tight.
Pros: Feels good, Can store things in grip.
Cons: Hard to install!
This review was written in the old system and had content requirements that are different than reviews written today.