VISM AR10 Upper Receiver Block Blue. The upper half of the block inserts into the AR10 receiver just like a bolt carrier group. The bottom half of the block can be bolted together with the upper block half with the provided steel bolts. This fully supports the inside and the bottom of the AR10 receiver and it also leaves the receiver optics rail open for mounting accessories and optics. The AR10 upper receiver block also has a hole through the length of the block to act as a bore brush guide for cleaning out the bore of the barrel. Specifications for VISM AR10 Upper Receiver Block: Manufacturer: VISM Gun Model: AR-10 Gun Make: AR Platform Gun Type: Rifle Color: Blue Weight: 29 oz Condition: New Package Contents: VISM Ar10 Upper Receiver Block What firearm models does the manufacturer say VISM AR10 Upper Receiver Block is compatible with? The manufacturer says that VISM AR10 Upper Receiver Block is compatible with AR-10VISM VTHAR10UVB: AR10 Upper Receiver Block Blue