PURPOSE: To prevent leakage of cooling water at the time of exchanging a tip and to improve fixation of the tip by providing a projecting part on the tip of a shank, fixing the cap-shaped tip attachably and detachably on the outside thereof and providing a small groove on the tip inside.

CONSTITUTION: A copper member with a projecting part is welded 25 to the tip of the hollow bar-shaped shank 20 to form the projecting part 22. When a recessed part 32 of the cap-shaped tip 30 is fixed attachably and detachably on the projecting part 22, a gentle taper 21 is provided on the projecting part 22, a lubricant 23 is interposed and the recessed part 32 is press-fitted and stuck to the projecting part 22. The electrically conductive lubricant is desirable as the lubricant 23. In exchanging the cap-shaped tip 30, since a waterway in a hollow part 24 of the shank 20 is not communicated with the air, the water leakage is not caused and when the cap-shaped tip 30 is fixed on the recessed part 32, since fluid materials in the space between the tip 30 and the part 32 leak to the outside from the small groove 31, fixation of the tip is improved.