The function of the roller is to transmit the weight of the locomotive set to the ground and roll on the track. In order to prevent derailment, the roller shall also be able to prevent the track from moving laterally relative to it.

The roller often works in muddy water and sand, and bears strong impact. The working conditions are extremely bad, and the rim is easy to wear.

The requirements for the roller are: wear-resistant rim, reliable bearing sealing, small rolling resistance, etc.