Absolute encoder can be divided to 3 types in mechanical: shaft encoder, end hollow shaft encoder and through hollow shaft encoder. Shaft absolute encoder needs some extra part like flexible coupling to connect the shaft of motor and the shaft of encoder. Hollow shaft encoder can directly mounted to motor shaft and fix it with screws, clamp ring and brackets. Generally, the bigger size encoder is alway with hollow shaft design. The hole is from 4mm to 50mm or more. Howerver, for shaft encoder, the shaft diameter is always from 4 mm to 15mm.

Rotary encoder is very important sensor in industry for feedback the mechanical angle, position, length, speed information. Absolute mechanical encoder is one of rotary encoder, which can supply the sole motion data to control system. There are mainly two types of absolute mechanical encoder: solid shaft absolute encoder and hollow shaft absolute encoder.