To provide the supplement rod of a high service life with good heat conduction efficiency by integrally providing a screw cylindrical part making an outside diameter equal to an intermediate part and cutting a female screw on an inner face on both the ends of the hollow rod of specific length.
A supplement rod 1 integrally providing screw cylindrical parts 3, 3 making an outside diameter equal to an intermediate part and cutting a female screw on an inner face respectively is provided on both the ends of the hollow rod of length of 500-1,200 mm, preferably 600-1,000 mm. A water hole 5 as a passage hole opened on both the same ends as the normal drilling hole rod is provided on the core part of the supplement rod 1. The supplement rod 1 is always interposed between a shank rod and the drilling hole rod as well as the normal connection rod, and used to supplement length in which a constant rod lacks. The supplement rod 1 is in a high service life with good heat conduction efficiency.
YOKOTA TADASHI
MURAMATSU KATSUSHIGE
MURAMATSU DOBOKU KK
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