I have two bit keys. One is stamped Master 53 and the other Master 53C. Does anyone know what company manufactured the locks that go with these keys or where these keys fit in the over scheme of the keys for the company? Judging from the appearenced it looks like Master 53 is the grand master and 53C might be the sub master. I was told that there were seperate bit keys for each interior door in the building and the Master 53 unlocked them all. I would love to learn more about the keys and locks related to them. If anyone can steer me to a good source it would be appreciated.