PURPOSE: To provide screw parts capable of simply inspecting the fastening condition as well as fastening with nearly predetermined fastening torque without using a torque wrench.

CONSTITUTION: In a bolt 1 provided with a head 12 fitting in a closed wrench W and a male screw part 13, projecting lines 14 engaging the closed wrench W to be stepwise crushed as rotational torque given to the male part 13 in the fastening direction is increased and escaping parts 15 are alternately provided in 6 corner portions in the head 12.