The AEM5 is the replacement for the iconic OPS INC 12TH MODEL that was used for the SPR/MK12 program. This is the suppressor you need for all your MK12's. A special barrel profile, collar and brake (sold seperate) are needed to mount this suppessor. This is one of the quiestest suppressors on the market in my opinion. All AEM5's are now knurled. These are available in the normal BLACK OXIDE. These are manufactured in Utah.