The 355001-TD Micro-Ion® Bayard-Alpert Hot Cathode Vacuum Gauge features a Tungsten filament for a 5 x 10^-10 - 5 x 10^-2 Torr vacuum measurement range, and a size NW16 ISO-KF fitting. Granville-Phillips® 355 Micro-Ion® Hot-cathode Bayard-Alpert Ionization Vacuum Gauges are the smallest Bayard-Alpert style gauges. They are more rugged and wider range than glass gauges. The 355 Micro-Ion® Hot-cathode Bayard-Alpert Ionization Vacuum Gauge requires only 8% of the power of a glass gauge, which means less heat to potentially disturb a process or experiment, cause accidental burns, or melt wiring that may come in contact with the gauge.