What is the outer diameter of the ppr4 water distribution pipe?

It depends on whether the water pipe is a PPR pipe or a thin-walled metal pipe. If it is a PPR pipe, the outer diameter of the 4th pipe is 20mm, and if it is a thin-walled metal pipe, the outer diameter of the 4th pipe is 15mm. The name in charge of 4 is the name of the imperial unit, because PPR pipes have a wall thickness problem, and the wall thickness of thin-walled metal pipes is generally negligible, so there will be such a difference.