dophee 20mm Dovetail to 11mm Extension Weaver Picatinny Rail Scope Mount Base 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). The top is fit for 11mm(0.43" approx.)rail. Bottom dovetail rail width: 20mm (0.78" approx).