It works for commercial spec stocks but it is tight - Sniper Commercial Spec 6 Position Aluminum Receiver Extension Tube and Buffer Kit

It works. Not great, but the price is very hard to beat and the tube construction is good but the OD does feel a little bigger than other Commercial tubes because the stock was a very very tight fit.

Castle nut was fine, end plate was sliding out of the key way so use a different end plate. The tube itself is decent enough, its "enhanced" which basically means its more annoying to get it threaded in to hold down the retaining spring. Buffer is weighted right 3oz, but the material of the buffer housing is sus.