Beautiful knife @DirtySouth ... Buy with complete confidence, Tommy is a stand up guy, and straight a straight shooter!
Thanks for the plug Mike. It is a nice knife, I just don't carry it enough to justify and need to raise some funds for a new camera.
What's the difference between this and the 21? ETA: I decided to do some research and found the differences. Thickness, finger groove, and dual thumb studs.
The jist of it, it is more of heavier duty knife with more solid lock up, along with the differences you found. That's not saying the 21 is a slouch and/or weak, it's just more of a classic gentleman's knife.