3/4″ Hot Water Meter with 3/4″ Male NPT Couplings. Ideal for 1/8-20 GPM flow rates on 3/4″ hot water lines. The smallest 3/4″ meter available on the market and it has a fully revolving dial for ease of reading. For domestic hot water use only. If the water temperature is above 160F, the meter must be installed horizontally with the register facing upwards.