The 355001-TH 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 1/2 inch male VCR 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. Plus, it has an x ray limit equivalent to that of a glass gauge (3 x 10-10 Torr). 355 Micro-Ion® Hot-cathode Bayard-Alpert Ionization Vacuum Gauges' dual, burn-out resistant, yttria-coated iridium filaments provide long life.