This is a Yankee Hill Machine Co Mount known as the Scope Riser, model YHM-227A.
This scope mount is perfect for varmint rifles. Great for all types of scopes" red dot sights" and other optics. Raises the equipment one half inch. Mounts to any picatinny rail" made from aircraft quality aluminum and hardcoated to military specifications.5-1/4" long.
Features:
Mounts to any picatinny rail
Adds 1/2 height;Aluminum construction