Flylock 3 3/8" Single blade Black waterfall switchblade knife

Antique Flylock 3 3/8" Single blade Black waterfall switchblade knife made at the Challenge Cutlery Co of Bridgeport, CT sometime between 1920 and 1928. This was originally a Flylock Letter Opener, but someone cut/ground the letter opener off leaving a small single blade automatic knife. I've seen it done many times and it makes sense to turn it into a useful pocket knife. It measures 3 3/8 inches closed and 5 3/8 inches open with brass liners and nickel silver button. The spear point blade is 98% full with light scratches and spotting and the tang is stamped Flylock REG US PAT OFF on the front and FLYLOCK KNIFE CO B'PORT CONN on the back. The scales are black waterfall celluloid and in very good condition. Knife works well with blade tip below liners closed, good snap and fair lockup with 3/16" up and down and a little side to side at the tip. Rattles if shaken with blade open. VG- condition.