Relton PC20 Porcelain Cutter 1-1/4" Finish Hole Diameter For Installing: Reverse Osmosis Systems Hot-Water Dispensers Spa Jets in pre-existing bathtubs Drill through porcelain and cast iron with pilot bit. Drill through porcelain only with spring-loaded saw. Drill through cast iron with finish saw. Relton Porcelain Cutter Kits are designed with the Finish Saw 1/8" smaller in diameter than the Porcelain Saw. The Finish Saw diameter is used to determine which kit should be purchased.