EX50 Track Lower Bottom Roller For HITACHI Excavator Undercarriage The function of the roller is to transfer the weight of the locomotive group to the ground and roll it on the track. To prevent derailment, the roller should also be able to prevent the track from moving laterally relative to it.rollers often work in mud and sand, and withstand strong impacts, the working conditions are extremely harsh, and the rim is easy to wear. the requirements for the roller are: the rim is wear-resistant, the bearing seal is reliable, and the rolling resistance is small. Our products are according to the standard of OEM to manufacture.