1221-M400-W/M is a series 1221 Flex-Tube® U-tube manometer which combines the inherent accuracy of the "U" Tube with the durability of tough, long-lasting plastic construction. The columns are made of 0.375˝ O.D. flexible and shatterproof clear butyrate tubing and are backed by a white scale channel to provide maximum color contrast. This manometer is ideal wherever a portable, direct reading manometer is needed. The Series 1221 Flex-Tube® U-tube manometer is a lowest cost basic U-gage. A dependable U-tube manometer that withstands hard use and provides accurate, high visibility readings. For use with water, mercury or red gauge fluid. For mercury filled manometers, a scale clamp bar, Dwyer® Part No. A-363 is recommended. One pair of carrying plugs and a pair of non-kink vinyl tube connectors are included with each manometer.