Phase 5 Weapon Systems AR15 Pistol Buffer Tube Complete Assembly, Black Finish PBT-CA AR-15 Pistol Buffer Tube Complete Assembly (PBT-CA) by Phase 5 Weapon Systems Inc. partners their enhanced buffer spring" billet aluminum Pistol buffer tube" Mil-Spec end plate" Mil-Spec castle nut" Mil-spec carbine buffer and their ultra-durable NPVC-constructed buffer tube foam pad. The lower slot is machined to accept all Mil-Spec end plates and sling mounting accessories.