Excavator Undercarriage Spare Parts EC210 Front Idler Roller fit for Volvo The function of an idler is to guide the track links into running smoothly and to prevent dislocation,idlers also carry some weight and therefore increasing groud pressure.there is also an arm in the center which supports the track link and guides the two sides.the smaller the distance between the idler and track roller,the better the orientation. Our products are according to the standard of OEM to manufacture.