Single Thoria Coated, IR Granville Phillips 274, Iridium Filament, Bayard-Alpert , KF25, ISO NW25, 3/4 in, Glass Ion Gauge, GP PN 274032  These Granville Phillips Iridium glass ion gauge tubes have a KF25 ISO NW25 Inlet, and a 3/4 inch vacuum connection port with an operating range from 1x10-3 to 2x10-10 Torr. These ion gauge tubes are compatible with most modern hot cathode ion gauge tubes. They have a sensitivity of 10 Torr-1 and standard operating voltages (collector 0 VDC, Grid +18