This is a Griffin Armament Adapter known as the Barrel Adapter, model PI1228.
The Griffin Armament CAM-LOK(TM) interface affords the user the ability to convert the suppressor to a much faster and more secure mounting solution on browning style action (tilt barrel) pistols vs it's legacy technology" single piece" direct thread piston counterparts. This system provides a rapid" secure attachment to the host pistol.
Features:
CAM-LOK™ (Covert Application Mount - Locking) Patented Universal QD piston attachment system
3 mounting positions, 120 degrees separated for rapid mounting
Forward taper surface locks in place with interfacing piston and drastically reduces or eliminates common baffle/end cap strikes
Coarse threads are top cut to increase durability and wear resistance
3/4or 19mm wrench pattern accommodates socket wrench for secure and easy installation;Compatible with Universal QD pistons (sold separately);Internal bore reduces side concussion and visual disturbance vs blind muzzle;Total system weight is identical to legacy direct thread pistons;QPQ Nitride finish for attractive, durable black finish;17-4 stainless steel material;Also supports Universal Carry Comp