About half way down the link, pg28 of 53 according to scribd or pg50 of the actual book... http://www.scribd.com/doc/35163521/08-Sheet-Metal-Work As said, like a backstop but reversed for times when the work is tiny and doesn't pass far enough through the machine for an actual backstop to work. Very occasionally they can also be useful for folding things with returns that'd usually interfere with the bending apron/leaf/beam... kinda like an inside out box and pan but different and just like a box and pan half the time the return (or sides of the box etc) you need is longer/deeper than possible and you wish you had the room/money for a press brake
Ok. I see. So stops to limit insertion, the part above the level of the bed will bave to be the same as or less than the thickness of the material being folded.