Seat belt retractor and method of producing the same

A seat belt retractor comprising:

• a housing including a pair of opposed side walls;
• a winding drum on which a webbing is wound, the winding drum being located between the pair of side walls and rotatable in a winding direction for winding of the webbing and in a pull-out direction for pull-out of the webbing, the winding drum including a central hole opening at least in a first axial direction that is one of opposite axial directions of the winding drum;
• an annular holding member located in the first axial direction relative to the winding drum and rotatable relative to the winding drum;
• a locking base mounted on the holding member, rotatable together with the holding member, and configured to be prevented from rotating in the pull-out direction in a vehicle emergency, the locking base including
• a main body portion located across the holding member from the winding drum in the first axial direction, and
• a shaft portion projecting from the main body portion into an interior of the holding member and including a male thread on an outer peripheral surface of a portion located toward a distal end of the shaft portion, the shaft portion being coaxial with the winding drum;
• an impact energy absorbing member including a first end and a second end, coupled to the winding drum at or near the first end and to the locking base at or near the second end, and configured to, under a normal state, connect the winding drum and the locking base such that the winding drum and the locking base are rotatable together, the impact energy absorbing member being further configured to, in case that a pull-out force applied to the webbing exceeds a predetermined level while rotation of the locking base in the pull-out direction is prevented, plastically deform to absorb impact energy while permitting relative rotation between the winding drum and the locking base;
• an impact energy absorbing wire received in a slot located in the winding drum, the slot having an opening facing in the first axial direction, the impact energy absorbing wire including a head portion protruding from the opening of the slot and attached to the holding member, the impact energy absorbing wire being configured to, during relative rotation between the winding drum and the locking base, be pulled out from the opening of the slot while plastically deforming to absorb impact energy;
• and
• a stopper member held in the central hole, unable to rotate relative to the winding drum, movable in the first axial direction and in a second axial direction opposite to the first axial direction, and screwed on to the male thread of the locking base, the stopper member being configured to define an allowable amount of relative rotation between the winding drum and the locking base during impact energy absorption by the impact energy absorbing member, wherein
• the locking base is mountable to the holding member in a plurality of mounting positions that are orientations defined by rotation about a rotational axis of the winding drum, and
• a dimension of an inner contour of the holding member, as viewed in the first axial direction, is greater than a dimension of an outer contour of the stopper member.