Rollpin, part T9, excisted in 2 lengths: 9 and 12mm. This part apparantly has been hardly used and therefore it became already obsolete somewhere in the mid 1960's.

Part T9 can be used to lock a hubdisk, gear or pully on an axle when the torque is considerable. A drill of 1.5 to 1.6mm or 1/16'' should be used in the drill starter hole, see the yellow square below, to make a seat for the rollpin.