Here is a link to a video of a similar vice setup and use:http://www.youtube.com/watch?v=4KSZou1AvtQ
At the end of the first video is the opportunity to go on to the jaws adjustment (left side, 2nd down)
Jaw adjustment is critical:
1 Use the small wheel nearest to the jaw points to make the jaws wide enough for your size of hook
2 Move the cam lever from pointing at you, through 45 degrees only towards the point of the jaws - this should exert a weak grip on the hook which will still move if you wiggle it with your fingers
3 If the hook is solidly held at this point you need to widen the jaws a little with the small wheel near the jaw tips.
4 When the halfway cam lever position holds the hook loosely as in 2 you may complete the movement of the cam lever a further 45 degrees until it is in line with the hook in the jaws and the hook will be rigidly held.
5 Never force the cam lever into the locked position - this WILL snap the jaws! The bigger the hook the more important this is.
If the proper care is taken using this vice it will not fail. The onus is on the user to have read the instructions and warnings above. Damage resulting from failure to read or follow the instructions will not be accepted as a valid reason for complaint/return. If in doubt, email an enquiry, consult the video, or perhaps choose a non-cam vice model.Many thousands of tyers use them, but many do so without proper care and experience 'surprise' failure of parts.