The structure is very compact and lightweight and they are particularly suitable for oxygen therapy. The body is made of brass and aluminium with an integrated calibrated orifices “dial” flowmeter having 10 preset medical gas flow options and it is housed inside a techno polymer shock proof shell to protect the assembly, while a large ergonomic control knob with Soft Grip inserts allows the operator to easily adjust the gas flow between the 10 possible preset options. They are equipped with a preset overpressure safety valve, and can be supplied, as an option, with a terminal unit connected to the first stage chamber which allows to get an additional and separate source of medical gas. The inlet connection is offered in several options, as per the different reference standards of the destination Countries. The outlet is through a nipple having two connection threads on the two ends for an easy and quick interchangeability. The operators can get two options of outlet thread by simply reversing the nipple, depending on the required applications.