To provide a knob for a fastener which is easily used even by an elderly person, a person with physical disability or a person who has long nails or artificial nails by setting an area of the knob in a direction orthogonal to its operating direction to be wider than the width of a fastener body, relating to the structure of the knob of the fastener such as a bolt ring or a swivel.

In the fastener such as the bolt ring or the swivel which has the nearly annular fastener body having a notch cut off at one end, an opening and closing member built in the fastener body and sliding in a direction in which the notch is opened and closed, and the knob formed integrally with the opening and closing member and projecting outward from the fastener body, the knob is composed of: a neck part passing through a slit at the fastener body; and a knob body which is formed of a wide surface whose width in a direction orthogonal to the opening/closing sliding direction of the opening and closing member is set to be wider than the width of the fastener body at the tip of the neck part.