central flange 12 and a base 13 the shank 11 has a truncated conical shape for insertion into a truncated conical hole 101 of a machine spindle 100 and fastening therein by means of a pair of keys 102 which are respectively engaged with corresponding recesses 103 on the flange 12 of the holder 10 the tip of the shank is cylindrically shaped the annular flange 12 has an annular recess formed in the outer surface a large diametral axial bore 14 for receiving shank 90 or adapter of a machine tool 91 is formed from the end section of the base 13 a small diameter threaded central hole 17 is formed from the interior end of the hole 14 to the opposite end namely to the top 18 of the shank the through hole 17 has a larger diameter at the tip portion than the remainder of the hole a threaded hole 15 is radially bored at a suitable portion of the base to open to the longitudinal bore 14 and another threaded hole 16 is radially bored in the same manner from the flange recess to the foregoing large hole 14 both radial holes 15 and 16 are at a right angle or are inclined at a u03b8 degree optional angle to the longitudinal axis a deformable thin ring 50 is movably engaged with a cylindrical portion of the base 13 between the side face of the flange 12 and the threaded hole 15 upon an annular ring 60 and a felt ring 70 as shown in fig2 for engagement of the annular 34 o 34 ring 60 a corresponding annular groove 61 is provided around the surface of the base 13 on the interior surface of the thin ring.