These are factory new Remington barrels made at the factory in Illion N.Y not after market barrels.This is the Police 18.5" for the 870 12 ga with IC fixed choke and 3" chamber, it is has a parkerized finish with the Remington pressed ramp bead sight and is the barrel that comes standard on the 870P model. As with all police barrels it has the detent plunger to retain the magazine cap or mag tube coupling. This is not an issue if you are putting it on the Express model as you magazine cap will simply push the detent plunger down and out of the way. Because of the Detent pluners it works with all Remington 870 shotguns and tube extensions. You would want a two shot extension with this barrel to give you a 6+1 Capacity. Does not work with the 870's that have the one piece 6 shot magazine tube. Note: If you wonder why the Parkerized Police barrels cost less then the Express barrels it is because they make more of the Police Barrels so the cost is less, so you are better off getting this for your Express because your Express Black Oxide finish was designed to look like Parkerizing so it will match.