XS Sight Systems Armorers Block for AR Platforms Black. This armorer's block will allow the gunsmith or enthusiast to assemble modify or maintain almost every AR pattern modern sporting rifle. While most blocks will only fit one specific style the XS block provides the versatility needed to work on any AR pattern upper and lower receiver: AR-15 AR-10 SR25 or DMPS GII. Includes pins to lock in the receiver. This versatility plus the reliability of an XS Sights made in specialized factories 6061 T6 aluminum product is a one size fits all solution. To allow bracing into the mag well of AR10 lowers XS has a 3D printed adaptor plate for purchase or home-printing. Will not work for ARs in .300 Win Mag or 12 ga. Specifications for XS Sight Systems Armorers Block for AR Platforms: Manufacturer: XS Sight Systems Gun Model: AR-10 SR-25 M4 AR-15 Gun Make: AR Platform Color: Black Additional Features: Upper Receiver & Lower Receiver Condition: New Features of XS Sight Systems Armorers Block for AR Platforms Includes pins to lock in the receiver; To allow bracing into the mag well of AR10 lowers XS has a 3D printed adaptor plate for purchase or home-printing; Will not work for ARs in .300 Win Mag or 12 ga. Package Contents: XS Sight Systems Armorers Block for AR Platforms What firearm models does the manufacturer say XS Sight Systems Armorers Block for AR Platforms is compatible with? The manufacturer suggests that XS Sight Systems Armorers Block for AR Platforms is compatible with AR-15 M4 AR-10 SR-25XS Sight Systems AR-7002AB-1: Armorers Block for AR Platforms Black