These specifications represent the thread diameter inside the connector and are used to connect water meters with corresponding diameters. Which connector size to choose depends on the required traffic and usage scenarios. DN 15 is suitable for small-flow water meters and domestic water, DN20 is suitable for medium-flow water meters and industrial water, and DN25 is suitable for large-flow water meters and large-scale industrial water. When purchasing the water meter connector, choose the appropriate size according to the actual demand.