This converter nut replaces the factory barrel nut. The Standard nut leaves a 1/4a ^2 gap, while the Modified nut leaves a 3/32" gap, but also requires permanent modification of your upper. Converter nut has the same 1.25-18 outside thread as most AR-15 uppers, allowing a wide variety of AR-15 barrel nuts and handguards to be mounted to your M&P 15-22. Black hard-coat anodized to a Type III MIL-SPEC specification.NoteThe "Modified" version requires permanent modification of your upper. The bottom handguard alignment tab needs to be removed and the top handguard alignment tab needs to be almost completely removed.The "Standard" converter does not require modification of your upper. If you are going to use a free-float handguard with an anti-rotation tab, use the "Modified" version.