Inside Ring Burs - 1/4" Head Diameter Size, shape, and cut are designed for fast deburring, smoothing and finishing of inside ring surfaces. Made of carbide steel for extra long life. Head diameter is 1/4" (6mm). 20-01401, 20-01402, and 20-01403 have 1/2" (13mm) head length and 3/32" (2.4mm) shank diameter. Available in 3 degrees of finish. Sold individually.