53a and the fixing nut 53b the procedure for replacing the flange members will now be described when a change from 36 spokes to 28 spokes is to be made for example front and rear pairs of flange members 32 and of 52a and 52b in which 28 spoke holes have been formed are readied along with front and rear rims inner positioning teeth 44a are formed around the inner periphery of each pair of flange members so that the spoke holes 43 will be shifted by one half pitch from one another the shape and number of the serrated inner teeth and outer teeth are the same for the 28 spoke flange members and the 36 spoke flange members first the tires 13 and tubes are removed from the front and rear wheels 7 and 9 the spokes 11 are removed from the rim 12 and the front hub 6 and the free hub 8 are taken out next the fixing caps 33 and 53a and the fixing nut 53b are loosened with a wrench and the flange members 32 52a and 52b in which 36 spoke holes are formed are removed from the hub units 31 and 51 in the assembly of the front hub 6 the front flange members 32 that have been readied with 28 spoke holes are mounted from both ends of the hub unit 31 of the front hub 6 at this point because the outer positioning teeth 41a and the inner positioning teeth 44a are formed such that the opposing spoke holes 43 are shifted by one half pitch the disposition of the opposing spoke holes 43 is shifted by one half pitch merely by the mounting of the flange.