Progressive Machine makes some of the finest product available. In this kit they provide the Extension tube, Nut, Spring, Follower and Barrel Clamp. Essentially everything you need to get the job done. All parts are manufactured in the USA.
This tube works on a M1/M2 and increases capacity 4 rounds making it an 8+1 total capacity to fit into USPSA 3 gun Competition Limited or Tactical Divisions.