AAC Brakeout. I run these with the CAR10-XH buffer setups from heavybuffers on my 10 SASS, two different 10 16" carbine's, and my 10 12" SBR. I also run them on my 5.56 guns also. Part is for the QD for the can, the other is for recoil without it. These things are nice, even if you didn't need them for the suppressors.