This is a used LaRue Tactical LT-660 Aimpoint Micro QD Mount.
Like all LaRue mounts, they are precision-machined out of bar-stock aluminum and matt black anodized to provide a durable non-reflective surface finish. The locking LaRue Speed Lever provides outstanding return to zero; the optic can be removed, and replaced, without loss of zero.
Allows a 1/3 co-witness with the Iron Sights on M4 Carbine and AR-15 Flattop.