Thornton knives date c. 1944-1949. They are not high quality knives and don't command much money with the exception of the picture handled knives they made. The picture handles were actual photographs under a layer of clear celluloid. The nude or cheesecake type photos will bring the most money.
If I have seen further it is by standing on the shoulders of giants.
I have one just like yours with red handles that is 3 5/16" overall length closed. I paid $3 for it at the local fleamarket. I believe the pattern would be called a shadow pen, as the pins go thru the handles and it has no bolsters.