61K64 - 

Grayhill 61K Series Optical Encoders, 4 Pin
The 61K series high resolution optical encoders offer either 25, 32, 50, 64, 100, 128 and 256 cycles per revolution positions. They have an extremely rugged construction and options include either pre-wired or with pins. They are extremely cost effective and have an operational expectancy of more than 10,000,000 rotations helping to reduce maintenance.