An improved housing is provided for a seat belt retractor mechanism. The retractor mechanism attaches to a seat belt retractor frame and has a belt rewind spring disposed therein which attaches at one end to a belt storage spool. The housing includes a housing body and a housing cap which rotatably abuts the body in covering relation and which engages the other end of the spring. The rotatable abutment is made possible by a plurality of socket members disposed along the outer periphery of the housing body and a plurality of resilient deformable locking flanges positioned upon the cap. The resilient flanges are formed on the cap in a manner creating a bias toward a position placing the locking fingers above the socket members when the cap is rotated relative to the body during the assembly process to tension the spring. When the spring has been sufficiently tensioned, the flanges are aligned with the sockets and deformed to an extent causing locking fingers on the flanges to latchingly engage the sockets. The combination of the latching engagement and the inherent bias in the flanges tightly affixes the cap to the body.