Motometers
by John & Henri Boggs.

Boyce - Midget Model.

A Boyce Midget model, 2-1/4" in diameter mounted on a die-cast zinc aftermarket accessory cap.  There is a latch to the left side allowing the motometer and cap to flip open to the right.

These caps are prone to cracks and did not hold up well.  Some aged better than others as a result of differences in the zinc batches that the caps were made from.