PURPOSE: To prevent a washer from being loosened so unnecessarily when a screw is unclamped as well as to facilitate the connection of external wiring by using such a washer as making the distance of an opening end, whose U-shaped double ends are bent inward each, smaller than the width of a thread terminal.

CONSTITUTION: In electrical parts including a photoconductive relay 1 or the like, a base part 5c being held between a thread terminal 3 and a screw 4 is installed in a washer 5. In addition, an arm part 5b is projected in direction of the thread terminal 3 vertically from both ends of this base part 5c. Likewise, both U-shaped ends consisting of the base part 5c and the arm part 5b are bent inward each and each of tip arm parts 5a is formed up, while a distance between these tip arm parts 5a and 5a is set to be smaller than the width of the thread terminal 3. With this constitution, when the screw 4 is loosened, the arm part 5b is made contact with the thread terminal 3, thereby preventing unnecessary looseness in the washer 5 from occurring, so that connection of external wiring to an interval between the thread terminal 3 and the washer 5 is simplified and ensured in this way.