4 points" is the name of the imperial pipe diameter length, that is, 1/2 inch. It is equal to 12.7mm in the metric system.
Unit conversion between pipelines:
4 in charge: 4/8 inch: DN15;
6 in charge: 6/8 inch: DN20;
1 inch tube: 1 inch: DN25;
Two-inch tube: 1 and 1/4 inch: DN32;
Inch half pipe: 1 and 1/2 inch: DN40;
Two-inch tube: 2 inches: DN50;
Three-inch tube: 3 inches: DN80 (also marked as DN75 in many places);
Four-inch tube: 4 inches: DN100;
De mainly refers to the outer diameter of the pipe, generally marked with De, which needs to be marked in the form of outer diameter X wall thickness;
Mainly used to describe: PVC and other plastic pipes, and other pipes that require a clear wall thickness.