One of the problems I have with a traditional face vise is its tendency to rack when a workpiece is clamped on only one side. To eliminate this problem, I used a few scraps of wood to make an adjustable, anti-racking block.
You can see how to configure the legs for the common stock thicknesses of 1⁄2", 3⁄4", 1", and 11⁄2". You do this by turning the legs face-to-face or edge-to-edge. The top holds the legs in position and keeps the assembly from slipping through the vise as you tighten it on the workpiece.
I used commonly available rare-earth magnets, cups, washers, and screws and installed them flush to the surface. Just make sure the magnets mate with the washers on the opposite workpiece.
