The 355001-TK 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 NW40 ISO-KF fitting. Granville-Phillips® 355 Micro-Ion® Hot-cathode Bayard-Alpert Ionization Vacuum Gauges are more rugged and wider range than glass gauges. 355 Micro-Ion® Hot-cathode Bayard-Alpert Ionization Vacuum Gauges offer a host of advantages over glass gauges. At less than 5% of the volume of a glass gauge, it mounts in almost any location on your system. Its all-metal design eliminates costly downtime that can result from glass gauge breakage.