Dwyer Flex-Tube U-Tube Manometer - Fluid FilledThese inexpensive manometers measure positive, negative and differential pressures. Dwyer Flex Tube U Tube Manometers combine the inherent accuracy of the simple "U" Tube with the durability of tough, long lasting plastic construction. Columns are of . 375" O. D. flexible and shatter proof clear butyrate tubing. They are easily accessible for cleaning. Indicating tube is backed by white scale channel to provide maximum color contrast. Scales are