Ian, the slot on the end of the phillips driver is for opening certain kinds of cans. Hams,corn beef as well as some gas mask filters used to have a key to peel a strip from the side. some times the key would be missing or broken off. hence the slot on the phillips driver. I know the U.S. military had cans like this up to the mid 1980's. Hope this helps...

BOATMAN
John