Some aggregate spreaders have a roller at the bottom of the discharge gates which spins to assure an even flow of aggregate onto the asphalt. This roller (Figure 7‑33) ensures that an even amount of aggregate is spread laterally across the pavement. The roller must be straight, not warped, for the aggregate to be distributed evenly.

The discharge roller should be visually examined to ensure there is no mud or other debris caked on its surface. A string line should be stretched from end to end of the roller to be certain it is not warped. To check the end bearings of the roller for excessive wear, the spreader should then be turned on and observed for wobble in the roller or noise coming from the bearings as they turn.