Remington Tube Extension Bracket
Factory new Remington Tube Extension Bracket with Quick Detach Stud and Screw. This is the bracket for Modern Barrels made after 1990 and has the X stamped on it to indicate this. It retails from Remington for $37.16.
These do not come with the bracket screw but yours will work. I you need a screw I have them listed on the store here in this same category.The Replacement Screw retails for $5.47 from Remington. This is designed to fit Remington Factory Extension kits and not recommend as a support bracket for other extension.
If you have an older 870 or simply have put an older barrel on it you should stay in this category and look at the "Pre-90's" Extension Bracket. Read that to decide which Extension Bracket you need.
You may notice I give a lot of information on this site so reading through some of the listings can also be a learning experience as I don't want people buying the wrong item or buying something they may not need.