The 274058 Nude Bayard-Alpert Hot Cathode Vacuum Gauge features dual thoria-coated iridium filaments for a <3 x 10-11 to 1 x 10-3 Torr vacuum measurement range, and has a size NW40 ISO-KF fitting with a pin guard and locking strain relief. Bayard-Alpert (hot cathode) gauges provide pressure measurement based on the ionization of gas molecules by a constant flow of electrons from a filament. The number of ions created is directly proportional to the density of molecules. The ions are collected and measured by a vacuum gauge controller and converted to pressure based on the sensitivity of the gauge. nude Bayard-Alpert hot cathode vacuum gauges are the best solution to severe ionization gauge pumping problems.