STOP BLOCK

The stop block is a device used primarily in woodworking (and in metalworking to a lesser extent as well) to ensure that the piece of wood or other material being worked upon is kept a certain, constant distance away from the cutting blade by allowing force to be applied to the material being cut in a direction perfectly parallel to the blade. This cutting device is typically a table saw, although stop blocks can be used with a variety of other machines, including radial arm saws and band saws.

Stop blocks generally run in a track cut into the saw's cutting surface, permitting it to move in only one direction (hence ensuring that all force is applied perfectly parallel to the cutting device, keeping the cut in a constant, straight line).