Quick Release Scope Mount 25.4mm/30mm Cantilever Scope Picatinny Weaver Single Top Side Rail Ring Rifle Scope Aluminum construction and fits 25.4mm/30mm diameter scope install on 20MM picatinny rails. Size: approx. 135 x 45 x 62mm (lxwxh), ring inner diameter (without insert): 30mm, ring inner diameter (with insert): 25mm and rail size: 20mm Front ring top and both side feature picatinny for mounting laser flashlight and compact red dot and so on accessories. Black in color and weight is 248g and length between two rings: 45m