Well, no. Let’s call it an ‘ Adjustable Bench Hold-down’.
My version is based on a design from the turn of the 19th century. The slide arm is adjustable 6″, so it will clamp anywhere from 9″ to 15″ from the shaft. It uses a 3/4″ diameter hole in the bench top. The clamping pad is 2″ round hard maple.
As you can see, the hole needn’t be exactly 3/4″. It will work in square dog holes or holes 1″ and above. The whole device is very ruggedly built of steel and hard maple. No need to lay out your work on the bench top so it is’within reach ‘ of your holdfast. You have 6″ of adjustability here. No need to grab that hammer (or sledge) to set it. The 5/8″ screw loosens and tightens very smoothly and can give just the right amount of pressure. No need to always have a back up pad to keep from marring your stock. Our pad is end grain hard maple.
Some other features I have noticed since working with it for the last few months is that it doesn’t tend to egg the hole in the bench top out as much as a holdfast which must be driven down and cocked every time it is set. It also holds well in benches as thin as 1 1/2″ . I tried it in a beam I had that was 5″ thick, so I don’t know what the upper limits might be. With the arm extended out, I don;’t think it matters how thick the bench is.