If you've taken advantage of CMMG's shortened, SBR-style barrel designed for the FN PS90, then you've got a correctly-sized SBR that looks like the famous P90. However, there are odd threads at the muzzle end of the barrel that need to be dealt with, and CMMG also has a solution for that in its PS90 Thread Adapter. The standard threads on an FN PS90 barrel are M12X1.0LH threads, which are copied in the shortened CMMG SBR barrel. However, this thread pitch isn't compatible with most muzzle devices on the market. To solve that problem, CMMG developed its PS90 Thread Adapter, which converts these threads to a more typical 1.2-28 TPI thread pitch.