The ST-3X Rifle Chassis stock is CNC machined from billet aluminum with a skeletonized body, vertical adjustable butt pad & cheek rest. It also features M-LOK slot and two QD disconnect sling mounts. The ST-3X is compatible with your rifle chassis systems with buffer tube style stock attachment. NOT compatible with AR-15 rifles or other rifles with a moving buffer system. The RA stock is designed to only work with a rifle chassis that accepts a buffer tube style stock.