| 摘要 |
<p>A step drill includes a body with an integrally formed handle, in which a spiral-form groove extends from the end to the front of the body, and the groove bottom is a paraboloidal structure. The combination surface of adjacent diameter is concave arc surface, or the combination surface of adjacent diameter is inclined surface, and the angle between the diameter of one side and the inclined surface is 43-47 degree.</p> |
