The HAL-LOCK outrigger pulley was specially designed for speed and efficiency (and it looks good too). Simply pull the locking lever back and the halyard is pushed into the softer urethane insert locking the halyard in place. That Easy! That Fast!, and because of HAL-LOCK?s unique ability to lock, very little tension is required on the shock cord, allowing you to get your clip up and back down with less effort. Finally, you don't have to rig up a configuration using rubber bands, wire and swivels. These components are both unsafe and ineffective. Just leave it to HAL-LOCK and the job is much more safe efficient and easy. The sizes (6, 9 and 12)refer to the length of the shock cord and snap on the various models.