TruSpeed Vintage 8K 8000 RPM Tachometer - Marine Boat Nautical

Description

I do not know what this TruSpeed Tachometer originally came with.
Good Cosmetic Condition (some scratches on lens).  Chrome Housing Quite Nice.
I tested this on my 12v 8 Cylinder Tach testing jig and it does function, but the RPM registered high.
I am not sure of the # of Cylinders it was designed for though.
The label on the back has:
TYPE   312501
AM      11/21/68
The OD of the base mounting plate is 4".
The OD of the chrome bezel immediately around the lens is 2 15/16".
Thanks for looking and Good Luck, Pete