1,Wheels of comparatively dense, 2,high in grain ratio (structure No. ... -F180 are used.3) GradeGenerally, harder grade (grade L-Q) wheels are used because of the grinding condition and other constraints ... . However, impact resistant wheels such as resinoid (B), rubber (R), and urethane (UP) bonded wheels are also used. Mounted Wheels and Screw-on WheelsKeihin ...