This is a Warne Scope Mounts Mount known as the Quick Detach, model QDXSKEL1TW.
Warne's 1 piece QD XSKEL cantilever mount features Patent Pending Dual Quick Detach levers and is constructed from 6061 T6 aluminum for a lightweight and rigid foundation. Steel threaded inserts ensure steel on steel contact between all threaded interfaces" and MSR Ideal Height helps the shooter maintain a proper cheek weld and shooting position with any optic on flat top guns. The QDXSKEL gives you a generous forward cantilever for modern scopes while reducing weight with its skeletonized design" and the Return-to-Zero performance that Warne(R) is known for.
Features:
Dual Quick Detach levers for fast installation and removal
Lightweight Skeletonized aluminum body and caps