Patent ID: 7074129

Claim:
A coupling member of a power transmission apparatus comprising a fiber reinforced plastic drive shaft to be coupled, the coupling member comprising: a fitting portion to be press fitted into the drive shaft, the fitting portion comprising an outer serration portion comprising serrations for digging into an inner circumferential surface of the drive shaft, the serrations including ridge portions, a cut away portion continuing from the outer serration portion, the ridge portions extending into the cut away portion, the cut away portion tapering at a first tapering angle, and a guide portion continuing from the cut away portion, comprising a free end, the guide portion tapering to the free end at a second tapering angle, a diameter of the free end of the guide portion being smaller than an inner diameter of the fiber reinforced plastic drive shaft, wherein the ridge portions of the cut away portion contact with an edge of and cut an inner circumference of the fiber reinforced plastic drive shaft when the outer serration portion digs into the inner circumferential surface of the fiber reinforced plastic drive shaft, and the first tapering angle of the cut away portion is smaller than the second tapering angle of the guide portion.