To dispense with a fastening tool.

A pair of holes 1b of an upper hole and a lower hole are formed at the tip of a torque arm 1, and a tapped hole 1c is formed in the middle. Along with forming a pair of holes 3b of an upper hole and a lower hole at one end of a calibration arm 3 at positions which correspond to the holes 1b, a hole 3c is also formed at a position which corresponds to the tapped hole 1c. Along with inserting positioning pins 14, 15 into the holes 3b, 1b respectively, a coming-off preventing pin 16 is inserted into a hole 1d which reaches the hole 1b from the tip of the torque arm 1, and a wing bolt 17 is inserted into the hole 3c and is screwed into the tapped hole 1c.