This instrument consists of a metal body, machined to have an internal chamber and one or more front windows (on one side only of the gauge).

On each window a special high resistance plate reflex glass is fitted with sealing joint and metal cover plates hold by bolts and nuts.
The chamber is connected to vessel with cross fittings and flanged, threaded or welded ends. Usually, between the instrument and its connecting ends, valves are fitted to consent shut-off piping and to disassemble the level gauge without  emptying  the vessel. Drain valves can also be fitted to cross fittings device.

To avoid leakage in case of glass breakage, safety ball-check device can be provided.