quite like these really, solid enough, like someone said they are not g-clamp tight. They come with no instructions, each clamp is made of two pieces, the section shown gripping the wood goes (A) into your workmate (fits my black and decker well), the second piece (B) has a lug that fits down the gap left between the leg of A and the side of the hole. The leg of A is cam shaped thus on when you insert lug of B where you can and then rotate it horizontally (clockwise I think) it cams the A tight into the hole at whatever height you have set. It doesnt cam the clamp downward but give a snug enough fit for extra grip on the work piece. Pretty good and unobtrusive when not in use.