Abstract: An inertial lock for a safety belt includes a frame supporting a fixed locking jaw and a movable locking jaw. The belt passes between the jaws. A spring yieldably urges the movable jaw into gripping orientation with respect to the fixed jaw to prevent movement of the belt between the jaws. The belt is trained about a wheel supported in the frame such that movement of the belt rotates the wheel. A shaft extends radially outwardly from the axis of the wheel, and a weight is reciprocably disposed on the shaft. A spring biases the weight away from the distal end of the shaft toward the rotational axis of the wheel. Centrifugal force on the weight caused by rotation of the wheel urges the weight against the spring. Wheel rotation rates in excess of a predetermined rate displace the weight radially outwardly along the shaft. The weight includes a mechanism for triggering the movable jaw to move in response to its spring into gripping orientation with the fixed jaw.