Attaches to the barrel and positions the scope back, over the receiver. Steel base solders to non-ribbed shotgun barrels only. Use Hi-Force 44™ Solder. MTF (machine-to-fit) Base - Hole spacing is drilled but barrel radius is left blank for custom fit applications. Mfg: Rbc SPECS: Base - steel, blued. Rail - aluminum, black finish. 5-¾'''' (12cm) long, 3.8 oz. (109g) wt. Mossberg 500 also fits M9200 and M5500. Ithaca 37/87 fits Deerslayer only, attaches to quarter rib. Includes instructions.