A pin is relatively rotatably fitted into a pin hole formed in an outer link plate of a chain. A plurality of helical grooves are formed on an outer circumferential surface of the pin. A pitch P between adjacent helical grooves in the axial direction is equal to or less than a width in the axial direction of the pin hole of the outer link plate. At least one helical groove is arranged to oppose an arbitrary generatrix on an inner circumferential surface of the pin hole. Also, when a radius of the pin is R and a relative rotation angle with the mating member is .theta., a pitch P' in the circumferential direction between adjacent helical grooves is R.theta. or less. Thus, at least one helical groove is arranged to always pass each position in a sliding range between the pin and the pin hole.