The bev block (barrel extension vise) is an all-in-one, compact vise block tool for ar15/m4 assembly operations of barrel nuts, flash hiders, etc.Mounts securely in a vise and provides support for both billet and forged upper receivers.Engages barrel extension with solid steel lugs and full-length support shank to prevent flexing.Steel hardness is optimized for durability yet won't damage barrel extension, and magpul polymer is used for all other engagement surfaces to protect aluminum receiver.O-ring post uses bolt carrier for additional stability and included pin keeps upper in the proper position.Type: Barrel Extension ViceColor: BlackMaterial: Polymer/SteelSize: Mil-SpecModel: BEVModel Fit: AR-15,M4,M16Caliber Or Gauge: 223 Rem,5.56 NATO