Maker's Name: 
Weston Elect. Inst. Corp.
15.3 × 3.2 × 4.7 cm

Weston meters are designed to use current shunts having a voltage drop of 50 milliVolts at the full current rating of the shunt. This shunts carries a maximum current of 3 Amps. It has 4 terminals, two large ones for connecting to the circuit carrying current, and two smaller ones for connecting to the shunted indicating meter, 50 milliVolts Full Scale deflection (FSD).