Yes it's for a door lock. I've got some old builders & locksmith catalogs that show a lot like the one you have. Started cutting the wards for these around 50 years ago in my Grandfathers shop. Still have buckets & buckets of keys that I've been putting off sorting for like 25 years. Value wise, $12 - $25 (antique stores around here). Markets dropping off since they're not the fad thing for crafters anymore. If you find the lock, they're simple to restore! The only thing that fails in the is the spring steel piece. Yours is pretty good shape for dug!