Main page » Inch and millimeter values for pipes and nozzle holders

The reason is the relationship to the inside diameter of a pipe. Because at the beginning of the 20th century, the technical manufacturing and steel options were even more limited than today. The clear width at that time of 1 "- ie 25.4 mm - required a corresponding wall thickness, so that the outer diameter expanded up to approx 3.8 to 4.0 mm and an external dimension of approx. 33 mm. The fittings and tools were also manufactured from this context. When the steel quality was improved, the pipe walls could also become thinner. However, because the fittings and threading tools were manufactured according to the outside diameter, the inside diameters had to become larger. In heating and sanitary engineering, the customs values ​​no longer correspond to a measure at that time, because the pipe dimensions with customs information are now defined metrically. In terms of language, the terms are of course still present. If you now find a tube with an outer diameter of ~ 33 mm, then the designation is and remains »1-inch tube«. The DIN EN ISO 228-1 standard specifies the thread identifier. The inside diameter of the pipe is not described in the standard. So you cannot convert from inches to mm. It is certainly not easy to keep track of things, but you should take into account the basic German style and prefer to use somewhat more stable dimensions for the application, because we are all familiar with that.