The inner diameter of the Dn160 tube is generally 160mm, and the thickness of the wall tube is 5mm, so the outer diameter=inner diameter+2×wall thickness=160+5×2=170mm.
The specifications and products of the pipe are determined by the outer diameter, so the DN and inner diameter of the pipe do not exactly match, and the inner diameter has a great relationship with the wall thickness. For example, DN25 is connected with Φ32×3 pipe, and the actual inner diameter is 26mm.