Many woodworkers use stop blocks and fences to make repeat cuts accurately. Alan Turner's spacer-block techniques take that concept a step further. He shows you lots of ways to use them to move a workpiece exact distances for cutting, boring, mortising, and other tasks. Using spacer blocks, you can move a workpiece closer to, or farther away from, the blade or bit, locking in a final setting on the fence and then taking multiple passes as you remove spacer blocks. Try them, and your mortise-and-tenon joints will be more accurate, your bridle joints will fit their slots perfectly, and your other joinery will fit without fail.

From Fine Woodworking #226