I have to admit that needed to go to my Ruana book to find it but I did.

This is a Model 21A and shows in the 1940 & 1944 catalog with a single pin. It's on page 91 & 94 of the "Hear the Hammer" Ruana guide book. The next catalog in the book is from 1962 and the 21A has 2 pins.

You should contact the Ruana shop as they may be interested in this early Rudy Ruana knife. Even with the age and wear, it is a rare Ruana. Nice find, what is the history on this one? We'd be interested in how you came to own it and what are your plans for it.