A hold fast being used to affix a board to the benchtop for chiseling dovetails
A hold fast is an accessory used on a woodworking workbench and in blacksmithing to fix a workpiece to the top or side of the bench while it is being worked.
A hold fast is shaped like a shepherd's hook. In use, the shank fits loosely into a hole in the top or side of the bench and the tip of the hook is pressed against the work. The hold fast is set by rapping the top with a mallet, which causes the shaft to wedge against the sides of the hole. It is released by hitting the back side.
A holdfast is also a plinth or pedestal, usually of concrete, to which an anti-aircraft or coastal battery gun was fitted. Holdfasts are often the only evidence for a weapon that survives.