AR-15/SIG556 Receiver Block (ARRB)
The ACE receiver block is perfect for most .22 conversion kits for the AR-15 and this will allow you to add a folding stock or an ACE Skeleton stock. This adaptor can also be used with short bolt carrier alternate recoil systems like Olympic Arms OA 93 or it can be used with SIG 556 (not compatible with SIG 556 Classic) and many other weapons that use AR-15-style M4 stock interface.
Features and Specifications:
Manufacturer Number: A501
Length .375" from back edge of receiver.
Weight 48g. (1.7 oz).