| 摘要 |
PROBLEM TO BE SOLVED: To perform mounting and demounting on a multi-step bit easily and speedily by forming a stopper by a ringlike object which has elasticity in the radial direction and of which free diameter is slightly smaller than a diameter of each step of the multi-step bit. SOLUTION: A stopper S is held by a lower face of an upper stepped part 2 in the axial direction of a multi-step bit. In the direction of its rotation, an end 18 which is bent in a longitudinal groove 19 is locked, and the stopper S is shrunk in the radial direction due to the action of a spring of the stopper S itself and is nipped and fixed on outer periphery of a desired stepped part 2 of the multi-step bit. At this time, it is preferable that a free diameter of each stopper S is slightly smaller than a diameter of the corresponding stepped part 2 and is engaged and fixed due to the action of the spring in order to improve the mounting property on a multi-step bit side. |
