These B-Square "Weaver" Adapter (2-piece) Bases are designed and produced the best mounts and rings to meet the special needs of rimfire and air gun shooters. The most notable is the adjustable "AA" mounts and rings. Usually the best mount for any airgun application, their unique design allows the adjustment of the scope to perfect alignment with the barrel, compensating for barrel drop, and putting the gun on target while maintaining the optical center of the scope. The mount also puts zero stress on the scope by self-aligning the ring saddles to the scope. 3/8" to "Weaver" Adapter (2-piece base)