61 b larger next some of the methods for attaching the pins to the shaft will be described as the methods for attaching the pins there are press fitting methods and insert fitting methods in a press fitting method a parallel pin or a spring pin is pressed into a hole of a shaft in the case of the structure in this embodiment a press fitting method is suitable for attaching the pins on the drive shaft 81 side however a press fitting method is not suitable for attaching the pins on the sleeve shaft 31 side in consideration of the removal of the coupling 61 and the assembly efficiency next an insert fitting method will be described with reference to fig1 a and 12 b fig1 b is a plan view of the driving force transmitting portion in fig1 a the diameter of the pin 32 is 2 mm whereas the diameter of the hole 31 p of the sleeve shaft 31 is rendered slightly larger than that of the pin 32 for example 2 1 mm the pin 32 is inserted into the hole 31 p of the sleeve shaft 31 after the coupling 61 is fitted around the sleeve shaft 31 next in order to.