Title reads "Brass Era Model T Ford Coil Box Switch Key and Carbide Gas Light Wrench"
What part is a wrench??
Ross - I think they are referring to the square opening on the tail of the key used to open the valve on an acetylene tank.
I wondered if that might be it (square opening) just never heard of it for that use. I thought it was to hang from or add to a key ring / tab/??
Mike is correct, it was in fact for the valve on Carbide tanks which were available factory options (along with Weed Tire Chains) on Model T's through 1914.
Thanks Mike and Royce, learned something new today. Good T trivia question . . .
Something like this?
These were more common.