Abstract: The mechanism includes a ratchet wheel, which is fixed to the spindle upon which a safety belt is wound, and a transfer ring, which is mounted around the wheel for limited rotation relative thereto. A tiltable synchronizing arm is mounted in a recess in the bottom of the ring for limited radial movement toward and away from the teeth of the ratchet wheel in response to an inertia trigger or pendulum member which is suspended beneath the arm. When the inertia trigger is operated, it tilts one end of the arm into the path of a tooth on the rotating ratchet wheel. When struck by the tooth, the arm is tilted in the opposite direction causing the opposite end of the arm to swing into the space between this tooth and the next successive tooth on the ratchet wheel, thus connecting the ring to the ratchet wheel. Further rotation of the wheel deflects the ring and causes it to pivot the inner edge of a locking bar into locking engagement with a tooth on the ratchet wheel to prevent further rotation thereof.