A protruding portion is formed on a rear side of a side plate, namely a side surface forming guide passage. The protruding portion is intended to prevent a thrust metal from being put to the guide passage with the left and right ends being in the wrong position. Accordingly, a height of the protruding portion is smaller than a depth of the oil ditch of the thrust metal, the width of the protruding portion is smaller than the width of the oil ditch. Also, regarding to the formation position of the protruding portion, when the thrust metal is truly set to guide passage, the center of the protruding portion approximately accords with the center of the oil ditch of the thrust metal.