5/16" cylindrical HSS burr on a 1/4" shank.
A rotary burr for deburring, weld dressing and blending in a die grinder or air tool. The head is 5/16" diameter with 1" of cut, on a 1/4" shank.
High-speed steel takes a keen edge and is more forgiving than carbide on softer materials and hand-held work, where a carbide burr can chip if it catches.
