This is a Accu-Tac Ring, model HSR-300.
The Accu-Tac Scope rings are Precision CNC machined to very tight tolerances on the height" center-line" and tube bed arch. For perfect alignment of the scope it utilizes a built in bubble level for perfect leveling of your rifle" and high strength hardware for durability.
Features:
7075 Aluminum alloy
Flat black
Hard anodize coating