||To make a holdfast, first remove
the fixed jaw from the clamp by drilling out the rivet that holds the jaw to the
clamp bar, as you can see in Figure 1.
Next, take a small metal strip and fasten it to the bar with a machine screw and
nut, as shown in Figure 2. Then to complete the holdfast, you can "lock" the nut
in place by crimping the threads of the screw at the end (Figure 2a).
To use the holdfast, just swivel the metal strip so it's parallel to the bar and
slip it through a dog hole in the workbench. Then swivel the strip back to hold
the clamp, as shown in Figure 3a.
I store my holdfast under the workbench so I don't confuse it with a regular bar
clamp and so it's handy when I need it.