Higoo 20mm to 11mm Weaver Picatinny Base, Dovetail Adapter to Extension Weaver Picatinny Rail Scope Mount Adapter Fits dovetail 11mm rail. Dovetail rail extension. Can be used to convert 20mm to 11mm. Sometime can be see through. All Matte Black finish. Material: Aluminum Alloy. Length: 58mm (2.28" approx). op Picatinny rail width: 11mm (0.43" approx). Bottom dovetail rail width: 20mm (0.78" approx).