in a low tension spiral conveyor belt system , driving assistance is provided between the driving cage or capstan and a plastic conveyor belt via ridges formed generally vertically on the bars or caps on the cage bars . these ridges , preferably rounded at their exterior surfaces , interact with grooves provided in inner edge members of the belt , or with gaps between successive edge members . as the belt progresses up the spiraling incline of the system , the drive capstan ridges seat in belt grooves or gaps for a short period of time , assisting in driving engagement , then advance forward out of the groove due to the overdrive relationship of the capstan to the belt .