Amazon.com: DIGITEN 4 Digital Green LED Tachometer RPM Speed Meter + Hall Proximity Switch Magnet Sensor NPN for Lathe Conveyor Belt : Industrial & Scientific
Jeti Telemetry Sensor RPM Opto MRPM EX
Engine RPM Sensor
Hobbywing, RPM Sensor, V-Bar system, Mikado - HOBBYWING North America