PURPOSE: To accurately and easily distinguish whether a screw is fastened under proper torque or not by looking with an eye.

CONSTITUTION: (a) shows a state where related members before fastening a screw are disassembled, and a washer 1 is a short thick cylindrical rubber member, and its initial outside diameter is smaller than the diameter of the head of the machine screw 8. (b) shows a state where the machine screw 8 is inserted, but before fastening the screw, and the outer periphery of the washer 1 hides itself under the diametral part of the head of the machine screw 8, and the washer 1 can not be seen from an upper side. (c) shows a state where the machine screw 8 has been fastened by proper torque, and the outside diameter of the washer 1 is laterally enlarged by longitudinal pushing pressure caused by a screw head, and the washer 1 is therefore forced out as much as a fixed dimension (a) from the screw head. In addition, the dimension (a) may be zero, namely the outside diameter of the washer 1 may be made to coincide with the diameter of the screw head, or the fixed quantity of protrusion of about 0.1 to 0.2mm is allowable.