The RBL 20 choke tubes don't have notches, they use a conical friction wrench. The muzzles of my RBLs, 20-gauge in the middle --

[Linked Image from i.imgur.com]

Here are the pages from the 2005 CSMC catalog announcing the RBL Launch Edition --

[Linked Image from i.imgur.com][Linked Image from i.imgur.com]