Quarter: DN15 (inner diameter 15mm), suitable for direct access to quarter (inner diameter 15mm) pipeline.
Sextant: DN20 (inner diameter 20 mm), suitable for direct access to sextant (inner diameter 20 mm) pipeline.
The 1-inch water meter is usually called DN25 water meter, which means that the inner diameter of the pipe used in the water meter is 25 mm.