I had fitment problems. I have this block on a 0.936&quot; bbl, with a Fortis Night Rail hand guard....at first it did not fit. The Fortis NR hand guard required modification to one of the guard openings to accommodate the leaf spring crew. I filed the offensive one opening larger and then &quot;thinned&quot; that guard section so that no contact with the screw for free floating. I chose to modify the hand guard instead of the screw. Make no mistake...this is a great gas block. The detente adjustment allows for crisp and positive settings for gas pressure. However, you may need to break out a file on your brand new handrail. I also had to remove the screw, detente and spring to get the handrail over the gas block and then re-assemble in place. Don't lose the detente! lol.