Spiralcool?âòÀÞ?â backing pads?âòÂìòÄâ exclusive rubber, fabric and fiber board construction provide extra strength and reliabilitySpiral ribs provide contact points and form channels for air flow extending discs life 30% to 50%Each pad is supplied with a nut as indicated, Additional nuts may be purchased separately.This backing pad is not to be used with SAIT-LOK?âòÀÞ?â quick change fiber discs.