The Trinity Force AR-15 mil-spec buffer tube kit gives you everything you need to mount a collapsible carbine stock on a mil-spec lower receiver. Stock is not included. Fit: AR-15 mil-spec lowers only - not compatible with commercial-spec lowers (commercial tubes have a wider diameter). Includes: Mil-spec diameter receiver-extension tube, 6-position, hard-coat anodized aluminum with rolled threads Carbine buffer (~3 oz) - H1 weight for a balanced gas curve Carbine action spring Steel castle nut, properly cut for stake-engagement Steel receiver end plate Aircraft-grade aluminum tube with hard-coat anodizing resists wear from repeated stock cycling. Castle nut should be torqued and staked per AR-15 build spec. Verify your lower is mil-spec before install; commercial-spec stocks will not fit this tube.