Centerless grinding describes a technique that holds the workpiece in the center between two grinding wheels, which rotate in the same direction (usually clockwise). The left side grinding wheel is held in position as it rotates. The direction of force applied to the workpiece by the left side grinding wheel is downwards towards the platform that holds the workpiece in place.
The secondary grinding wheel to the right is called the regulating wheel. It has the flexibility to move in response to the pressures applied to the workpiece between the two grinding wheels. The regulating wheel keeps the workpiece in place and turns it for grinding by the grinding wheel. This allows the grinding wheel to remove any excess material that remains after grinding in the first pass.