"The Portable Safe"
by the Automatic Recording Safe Co., Chicago, IL
Align the key cylinder as shown and then insert the key so that the single tooth points towards the rounded end of the hinged door. Rotate the key about 60 degrees clockwise to begin engaging the spring-loaded latch. Exert rotational pressure and continue turning the key another 30 degrees clockwise to take the tension off the latch and then pry the hinged door open.
The spring-loaded latch is shown in its normally-closed state. There is a bracket with a detent on the inside of the safe that traps the latch and holds the hinged door closed.
Here is a sketch showing critical dimensions of the key. The key blank is 1/32 inch thick and 3/4 inch long. The key is inserted 3/8 inch into the lock.
I do not know exactly how old my "portable safe" is, but I know that it had to have been made and distributed before 1941. Most likely, it dates from the second half of the 1930's.