This barrel is for the M10/45. It is 5-1/4″″ in length and double threaded 7/8-9 as well as .578-28 TPI. This barrel is ideal for situations where you want to use multiple accessories with different threads. Perhaps you want to use your old school MAC suppressor which is threaded 7/8-9 as well as your modern suppressor which is threaded .578-28. It is made of CrMoV MIL-B-11595 material with 6 – groove, 1:10 twist and precision air gauged with inert gas vacuum stress relieved after button rifling process. The finishing is manganese phosphate, the traditional dark gray/almost black parkerizing of the MAC series guns . These were profiled on centers to provide accuracy between bore and profile which has been a problem we’ve experienced with other manufacturers’ barrels in the past. These will fit Full and Semi Auto M10/45 guns.