Abstract: The disclosure provides a bolt including a main body, a head portion and a thread portion. The main body has a central axis. The head portion connects the main body. The thread portion is connected to the main body and runs around the central axis. The thread portion has a bearing surface facing toward the head portion. The bearing surface is a continuous curved surface or has an inflection point. The bearing surface includes a concave curved surface, a convex curved surface and a flank surface. The concave curved surface connects the main body. The convex curved surface is located further away from the main body than the concave curved surface. One side of the convex curved surface connects the concave curved surface, and another side of the convex curved surface connects the flank surface.

Abstract: The disclosure provides a bolt including a main body, a head portion and a thread portion. The main body has a central axis. The head portion connects the main body. The thread portion is connected to the main body and runs around the central axis. The thread portion has a bearing surface facing toward the head portion. The bearing surface is a continuous curved surface or has an inflection point. The bearing surface includes a concave curved surface, a convex curved surface and a flank surface. The concave curved surface connects the main body. The convex curved surface is located further away from the main body than the concave curved surface. One side of the convex curved surface connects the concave curved surface, and another side of the convex curved surface connects the flank surface.

Abstract: An arc shield is used in projection welding. The projection welding is performed for welding the lower end of a metal stud to the upper surface of a metal plate. The stud has a head and a stem connected securely to the central portion of the lower surface of the head. The arc shield includes an annular horizontal top wall defining a hole therein, and an annular vertical side wall having an annular top end connected securely to the outer peripheral portion of the top wall, and an annular bottom end having a plurality of notches. The annular side wall defines a chamber therein. The hole of the top wall has a size slightly greater than the diameter of the stem of the stud so as to allow for extension of the stem of the stud into the chamber through the hole of the top wall. When the projection welding is being performed, the electric arc is enclosed within the arc shield, while the surplus gas and molten metal that occur in the chamber flow from the arc shield through the notches of the annular side wall.