It looks like the one my Dad's old milk truck had in it.
6 cylinder engine.

Looks like the old Sun Tachs from years ago but the Sun name if not on the face.
This would be only a piece of the unit. The transmitter box would also be required The low Max. RPM reading does indiacte if from a truck or school bus.
As an example a tachometer was available as an option on a 1960 C60 truck with a V-8 engine.
Option # 266, $45.00 and would have been a Sun Tach. and probably less the Sun name.