When I put one on my son's Colt, of course the gas tube hole hit right in between two holes in the barrel nut. Strap wrench, some cussing, and God only knows what the torque is but it's on, it works, accuracy improved over the stock forend, and it has been OK now for about three years. The rubber is not that thick as after it was all on, we drilled and tapped the bottom of the forend for a sling swivel stud. The aluminum is pretty thick but if I recall the rubber was maybe 1/16 inch tops. The forend is a smaller diameter than the tube forend on my Armalite M15 A4 (T) but we like just fine. Personally, I think a larger forend would have looked goofy on the Colt with its A2 upper.