These sensors are for 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 angled tips have a 4" insertion depth. Each has four radially drilled .040" sensing holes. All except Model A-303 mount in 3/8" hole in duct. For portable use, a magnet holds No. A-303 in place. No. A-305 is used where a very low actuation or sensing point is required on a pressure switch or gauge or where response time is critical. No. A-307 and A-308 are suitable for use in low velocity systems or where the need for accuracy is less critical.