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The guide is a notched block of wood with two holes in it. Each hole has a metal bushing in it to protect the jig from being damaged by a drill bit.
Mark a 90-degree angle on a 2x4 for the notch. Use a band saw to cut the notch, then use a table saw to remove excess length from the 2x4.
Mark the center of each the side of the jig where you are going to drill the holes.
Use a drill press to drill the holes through the jig (Image 1). Use a bit the same size as the outside diameter of the bushings.
Turn the block over and drill a hole through the other side using the same bit. Carefully align the opposing holes, then fit the bushings into holes (Image 2).