Came off of remington 1100 tactical tac-4 model. Will fit 870, 1100, 11-87, Versamax, and V3 12ga shotguns.  Flush with muzzle of 22" barrel.  Includes new Wolff extra power spring,  grey follower,  and remington barrel clamp with sling stud (oem) 

These are impossible to find and regarded as being better than the aftermarket extensions.  Try to find another! There are some OEM +2 extensions on ebay for $180 - $240, none of these +4 extensions to be found.