Convenient kits contain all the components needed to securely mount the buttstock of your choice using original factory parts from the manufacturer of your receiver. Eliminates the hassle of tracking down every part and accidentally getting incorrect ones for your stock. Have everything you need to finish your build, so you won’t be held up waiting for that one part you forgot to order. Each kit contains original factory parts; parts from one manufacturer will fit another manufacturer’s receiver but may require minor fitting. Select the buttstock you want (available separately), then purchase the mounting kit for that type of stock. A2 Rifle kit is for mounting any fixed rifle buttstock based on the military M16A2 stock. Kit includes receiver extension tube, recoil buffer, buffer spring, buttstock spacer, and buttstock screw. HIGH STANDARD – Original parts used in the HSA-15 series of rifles and carbines. Commercial Carbine and fixed A2 Rifle kits available.