The common Model T key with the diamond shaped head was adopted by Ford in 1919. They were initially made of nickel silver until the switch was made to brass in 1926. On one side, they are marked with the Ford script and a maker’s mark like one of the following:
Briggs & Stratton
Clum Mfg.
King Lock
Caskey-Dupree
The original Ford technical drawings also list Culver Stearns as a manufacturer, but I do not recall having seen a key with that particular mark on it. The other side of the key is marked with the series number, and those numbers are 51 to 74 inclusive:
This number was also marked on the ignition switch found on the dash, a system that made stealing cars a simple task for thieves. This bit of advice was found in a 1920 issue of Motordom Magazine:
“On every ignition switch is a small number which corresponds to the number on the handle of your switch key. Organized thieves carry a complete set of these keys. A passing glance at the switch on your car gives them the number of your lock. They walk down the street, select the proper key, walk back, step in the car and drive away. A small file will in a moment or two efface the tell-tale number on the switch.“
If you are interested, the original Ford technical drawings and engineering release notes for these keys can be found in the digital collection on the Henry Ford website:
Drawing, “Ignition Switch Key,” Ford Model T, April 24, 1919 – The Henry Ford
Drawing, “Ignition Switch Key,” Ford Model T, December 19, 1919 – The Henry Ford
Drawing, “Ignition Switch Key,” Ford Model T, January 30, 1926 – The Henry Ford
Engineering Release Notes, Ignition Switch Key, Ford Model T, 1919-1926 – The Henry Ford
