Pretensioner

A pretensioner for a vehicle safety restraint comprising a piston (2), a cylinder (1) housing the piston (2), a force reservoir (12), activatable when a crash is sensed, to drive the piston (2) along the cylinder (1), a resilient band (7) connected to the piston (2), and means (7,8,9) for selectively connecting the band (7) to a retractor spool under predetermined conditions. The force reservoir (12) comprises a gas generator (12) which may be pyrotechnically activated and has an output in the cylinder (1) on one side of the piston (2) to drive the piston (2) along the cylinder (1) pulling the band (7) and engaging the connecting means (7,8,9) to turn the retractor spool and shorten the belt webbing.