Just what you need - Tacmod US Tactical Systems Back-Up 20 and A2 Buttstock Installation Kit

I wanted to add an A2 butt stock to replace the collapsible one. Of course the spring, buffer and tube are different on the M4 types, so I needed this kit. It comes with everything I needed, including the spacer. Well finished (although none of the parts are visible once installed) and good quality. Easy installation. Delivery time was great! What's to say? Good parts!