Bar Gauge Heads

This is a very old-timers tool that has never lost its superb function. It's particularly useful in drawer work and works most effectively as a "double-check" during final glue-up. You simply slide two narrow wood pieces (which you make yourself) through both Heads. Place the resulting "stick" diagonally across one dimension, tighten the Heads and then attempt to fit the "stick" across the other facing diagonal. If it fits precisely, you have an absolutely square construction.