This Truck Tuner reconditions your HO & On30 gauge railroad truck bearings so cars roll smoother with less friction. Simply insert the tool in place of a wheelset and rotate the shank. Truck Tuner's extra-sharp tool-steel cutter reshapes the bearing to the NMRA's recommended 60 degree contour and cleans out burrs and grime. Repeat for all bearings and your car is ready to really roll. Increases train lengths that locomotives can pull by up to 20 percent! For HO & On30 standard gauge trucks only.