The Dwyer A-303 Static Pressure Tips, 3/16" Plastic/Rubber Tubing, 4" (101 mm) Insertion Depth are for portable use with Manometers, Magnehelic gauges, Pressure Switches and other Controllers to pick up or sense static pressure drop across air filters and cooling coils, blower input and discharge pressures, etc. The A303 has a 4" insertion depth. Each has four radially drilled .040" sensing holes, and works with either rubber or plastic tubing at 3/16" or 1/8" inner diameter sizes. It uses a magnet to hold in place while in use.