Replace your existing front sight with this versatile gas block. The Picatinny-style rails are perfect for mounting flip-up front sights or other accessories to your AR. Simple installation with four included head cap screws. Requires gas block height front sight. Mounted by the use of four socket head cap screws using a 7/64" Allen wrench.NoteThis is a gas block height Yankee Hill Machine Gas Block. The Yankee Hill Machine Flip-Up sight (454763) is recommended by Yankee Hill Machine.