Armaspec SRS Buffer Kit Gen 4, Stealth Recoil Spring-H2, Fits AR-15, Black ARM263-H2 The Armaspec enhanced buffer tube kit contains all the necessary parts required to mount a stock assembly on to a lower receiver. The buffer tube kit" contains a mil-spec 7075-T6 6 position buffer tube" a steel castle nut and end plate as well as a SRS GEN3 the enhanced multi stage recoil buffer system .