The 274043 Nude Bayard-Alpert Hot Cathode Vacuum Gauge features a single thoria-coated iridium filament for a <3 x 10-11 to 1 x 10-3 Torr vacuum measurement range, and has a 2.75 inch non-rotatable CF flange fitting with pin guard. 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.