Pro Bore choke tubes are 12ga only.
Rem Chokes are Remington Factory Chokes for barrels that are threaded for Rem Choke Tubes. All 870 Express guns with threaded barrels except the Rem Choke tubes. Other Models may have Pro Bore Tubes which are Remington Factory Choke tubes barrels threaded for the Pro Bore tubes.
If you are uncertain which you have simply screw out your existing choke tube and look where the threads are. If the threads are at the back it is a Rem Choke tube. If the threads are at the front it is a Pro Bore tube. You can also compare it to the pictures of the tubes on my store.