On unmounted flap wheels, the flaps made of coated abrasive are arranged radially around the tool axis in a fan-type structure. Their flexibility enables them to adapt perfectly to the contours of the workpiece. The abrasive grain is embedded in the sturdy, flexible cloth backing material by means of a resinoid bond. In ISO 5429, unmounted flap wheels are designated as "flap wheels". For general applications from coarse to fine grinding.