Abstract: The spark gap portion of an ignition plug in a combustion chamber is adapted to be opposed to a bundle of streams of the air-fuel mixture withdrawn from an intake valve and is positioned on a line extending from the center of the cylinder to a midpoint between the intake valve and an exhaust valve, the spark gap portion further being positioned approximately midway between the center and the midpoint. The spark gap portion of the plug and the vicinity thereof are automatically cleaned at every stroke of the piston.

Abstract: A steel bar for concrete reinforcement has a non-circular cross-section which comprises two sets of transverse ribs disposed respectively at diametrically opposite surface portions of the core of the steel bar, each set consisting of a number of transverse ribs of a lug-forming projection type disposed at a position corresponding to every pre-selected pitch in the longitudinal direction of the steel bar and extending therefrom in planes substantially transverse to the core; and a pair of longitudinal ribs disposed on the diametrically opposite surface portions of the core at the intermediate positions between the sets of transverse ribs and extending from the core linearly in the longitudinal direction thereof; the outer portion of each of the longitudinal ribs being as remote as or less remote from the axis of the steel bar as compared with the distance between the axis and the surface of the portion on the outer circumferential plane of the core located at the remotest position from the axis; the major cent