Just when you think everything has been covered, you always manage to find another weird mechanism. This is a mechanism which I discovered on a Union block plane recently. The plane is a Union No.9½ with an “improved throat adjustment or slide, by means of which the opening for Cutter may be closed or enlarged” (Union catalog “Iron and Wood Planes”, 1905). The adjustment mechanism is a simple metal plate with a diagonal slot cut into it. Either end of the plate is bent at 45° to allow for adjustment. As the plate is moved from side-to-side, the threaded screw attached to the throat plate moves forward and backward, adjusting the size of the throat opening.