This gearbox is the same one used on our HD Hex Motor 40:1 Spur Gearbox featuring our 5mm HEX output shaft! This gearbox can be installed on any 550 series motors (like the NeveRest motors from AndyMark) giving you the convenience and flexibility of a compact gear reduction with an easier to work with output shaft. The hex output shaft is compatible with all of our gears, sprockets and wheels with NO more hubs or Setscrews required. The pinion gear is included to make it easy to mount any motor with a 3mm output shaft.