Abstract: To facilitate mounting the ignition plug socket into a socket mounting hole formed in an engine body and additionally to prevent vibration of the mounted plug socket, a plurality of projections such as axially extending straight ribs or circumferentially extending annular ribs are formed on the outer circumferential surfaces of the plug socket body of the ignition plug socket.

Abstract: To arrange and clamp plural high tension cords accurately and orderly in parallel to each other within a narrow space on an engine cover for prevention of the cords from vibration, a high tension cord clamp member is selectively and removably attached to a plug socket body, according to the number and the arrangement position of the high tension cords. That is, some cord clamp members formed with different cord holding portions and different cord holding cutouts portions are previously prepared and selectively mounted on ignition plug sockets according to engine model. Therefore, the high tension cord arrangement work productivity can be improved, because high tension cords can be previously assembled, before the plug sockets are connected to the ignition plugs, by use of the cord clamp members removably attached to the plug sockets.