PURPOSE: To keep screws and bolt parts from being blown backward by any impact even when a shot hits the screws and the bolt parts by fixing parts using a titanium washer together with the screws and screw fixing wares such as bolt and nut.

CONSTITUTION: To fix a part 11 on a shield body A, a bolt 14 and a nut 15 are used and a titanium washer is mounted inside the nut on the surface side. The bolts and nuts herein used are above M6 (the same with the screws) and box nuts are preferable in the respect of impact resistance. The titanium nut is preferably 10-30mm in outer diameter and at least 1-4mm in thickness viewed from the anti-elasticity and the balance of size. The titanium washer is arranged on the surface side normally together with the nuts. This keeps the screws, nuts and bolts from being blown backward by any impact thereby getting rid of dangerous spot called as dead angle in the past.