This is a Gear Motor w/Encoder, model No. GB37Y3530-12V-83R. It is a powerful 12V motor with a 131:1 metal gearbox and an integrated quadrature encoder that provides a resolution of 16 counts per revolution of the motor shaft, which corresponds to 2096 counts per revolution of the gearbox’s output shaft.
These units have a 0.61" long,