Simple, Effective, Cheap - SECTool! Woodworking jig for adjustable shelving holes. Drill quick and accurate shelf holes with this jig from reader John Ryan. Cut a 6 in. x 1 1/2 in. aluminum angle, and 6 in. x 3 in. and 2 in. pieces of 3/4 in. plywood. Screw the angle to the 3-in.-wide piece, then drill three 1/4-in. diam. holes 2 in. apart and 1 in. from the inside of the angle iron. The 2-in. plywood is the handle. Make a drill stop with 1-in. dowel.