US-DEALS Black T2ctical Polymer Picatinny/Weaver Front and Rear Combo Set Flip Up Backup AR15 AR-15 M16 M4 M-4 Flattop A1 A2 Post Back Up Sight Mounting decks designed to be used with handguard rails or front gas blocks (front sight tower) and both will fit all 7/8 inch Allen wrench with locking Retention for maintaining zero under heavy conditions Easy and quick installation