Abstract: A spark plug includes a metallic shell member having a tubular portion extending along an axial line of the metallic shell, a center electrode disposed inside the tubular portion and extending along the axial line, and a ground electrode which is inserted into an opening 5 provided in the tubular portion and forms a gap between the center electrode and a forward end portion of the round electrode in a direction in which the round electrode extends. A screw thread is provided on an outer circumferential surface of the tubular portion. The opening has a sloping portion which tapers from the outer circumferential surface of the tubular portion toward an inner circumferential surface side. An angle formed between the 10 sloping portion of the opening and a tangent line to the outer circumferential surface is 90 degrees or greater.

Abstract: A spark plug includes a metallic shell member having a tubular portion extending along an axial line of the metallic shell, a center electrode disposed inside the tubular portion and extending along the axial line, and a ground electrode which is inserted into an opening 5 provided in the tubular portion and forms a gap between the center electrode and a forward end portion of the round electrode in a direction in which the round electrode extends. A screw thread is provided on an outer circumferential surface of the tubular portion. The opening has a sloping portion which tapers from the outer circumferential surface of the tubular portion toward an inner circumferential surface side. An angle formed between the 10 sloping portion of the opening and a tangent line to the outer circumferential surface is 90 degrees or greater.

Abstract: The spark plug includes: an insulator having an axial hole extending in an axial direction; a center electrode disposed at a front end in the axial direction of the axial hole and having a front end portion that protrudes from a front side of the axial hole; a tubular metal shell holding the insulator; and a ground electrode having one end portion that is fixed to a through hole provided in the metal shell, the ground electrode having another end portion that forms a discharge gap between the other end portion and the front end portion of the center electrode. The through hole extends toward the front side in the axial direction, in a direction from an outer peripheral surface toward an inner peripheral surface of the metal shell. The one end portion is located on a rear side relative to the other end portion in the axial direction.

Abstract: This spark plug inhibits excessive increase in the temperature of a ground electrode to inhibit occurrence of pre-ignition. The spark plug includes: an insulator in which an axial hole extending in an axial line direction is formed; a center electrode disposed at a front end in the axial line direction of the axial hole and having a front end portion that protrudes from a front side of the axial hole; a tubular metal shell holding the insulator; and a ground electrode having one end portion that is fixed to a through hole provided in the metal shell, the ground electrode further having another end portion that forms a discharge gap between the other end portion and the front end portion of the center electrode. The through hole extends toward the front side in the axial line direction, in a direction from an outer peripheral surface toward an inner peripheral surface of the metal shell. The one end portion is located on a rear side relative to the other end portion in the axial line direction.

Abstract: In a grinding wheel truing method of an aspect of the present invention, an outer peripheral surface of a grinding wheel is trued while a position of a truer with respect to the grinding wheel is moved from one end side toward the other end side in the axial direction of the grinding wheel. In the truing, a relative movement speed of the truer when a position of the outer peripheral surface of the grinding wheel which grinds a large-diameter portion of a conical surface of a work is trued is lower than a relative movement speed of the truer when a position of the outer peripheral surface of the grinding wheel which grinds a small-diameter portion of the conical surface of the work is trued.