Hello, All:

I'm working with several old Yale mortise locks for interior doors. None of the 5 locksets have a key. The key is a skeleton-style key.

Can someone guide me as to where to look for the lock key code? Is it the stamped number inside the mortise box? In my case, the stamped number is 820 MK?

How do I use the number (if that is it) to locate a key(s)? Is the code 820? 820MK? 820 MK?

These mortise locks are old, have solid (not hollow) brass knobs and brass plates. I feel certain they are pre-1950.

Thanks to any and all!

Ed Rouze