Your post kind of confused me but here is the deal. There are two lengths of buffer tubes available for the AR15. They are the A2 and carbine length. The carbine length is the one used with the adjustable stocks and are commonly referred to as the M4 style stocks the other is used for fixed stocks. Before you choose which stock to use you must know which carbine length tube you have. There are two different ones and they are different diameters. They are referred to as Mil-Spec size which is 1.14" OD or Commercial size which are 1.17" OD. If you try to put a mi-spec stock on a commercial tube it will either not fit at all or it will be very, very tight and hard to extend. Also you must have the correct buffer and spring to match the tube you are using. They are also tagged as the "A2" and "carbine" models. Check out the offerings from MagPul they have some pretty nice stocks such as the MOE, CTR, and ACS. The MOE and the CTR are offered in either mil-spec or commercial but so far I've only seen the ACS in mil-spec. Hope this info helped.