Saw pictures of these in a book- funtionally similar to the rather expensive Bessey, but retained on the board to be edged by 2 rubber covered 'snail' cams. (bit like the joist grippers of the Record flooboard cramp). Looked a bit simpler to make than the Bessey (cheaper?), wondered who supplies them. Made by German coy, Würth, I think. Any ideas?