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Unfortunately, plywood can't be tapped and trusted to hold an air fitting under pressure, so 3-gauge steel was used to make a collector block-off plate. A Mr. Gasket collector gasket was placed onto the spare piece of steel and traced. The metal was cut (you can use a hacksaw or Sawzall) with approximately a 1/2-inch of additional clearance around the circumference of the gasket. The three collector bolt holes were made by drilling an 1/8-inch pilot hole, opening it up to a 1/4-inch hole, and finally to a 3/8-inch hole. Since the bolts' diameter is 3/8-inch, a round-file opened the holes further and provided some wiggle room for the bolt to fit through. Next, two 7/16-inch diameter holes were drilled on the face of the collector block-off plate and tapped with a 1/4-inch NPT (18-thread) tap.