from Lee Valley Tools for William for his computer to facilitate his changed posture. It is heavy and lacked good installation instructions. Whatever the fault, it basically broke off the desk today, being held on with four one inch screws. The main plate also has a central hole so I've bolted it to his desk. It is strong enough now, but there is a bolt sticking through the tabletop (not a big deal as I built this table myself out of plywood and will probably replace it at some point).