There are two main types of inertial seat belt locks. A webbing-sensitive lock is based on a centrifugal clutch activated by the rapid acceleration of the strap (webbing) from the reel. The belt can be pulled from the reel only slowly and gradually, as when the occupant extends the belt to fasten it. A sudden rapid pull of the belt—as in a sudden braking or collision event—causes the reel to lock, restraining the occupant in position. Automatic locking retractor for seat belts and shoulder harnesses in the U.S. was the Irving "Dynalock" safety device. These "Auto-lock" front lap belts were optional on AMC cars with bucket seats in 1967.