SCAFFOLDING TUBE DIAMETER CALCULATION?

Scaffolding tube diameter should be 38.1mm, but now generally by the metric series close to the election,
So the metric series should have a diameter of 48 mm. 4 points, 6 points, 1 inch is the British argument that inch.
Ordinary 4 tube 1 \ 2 “— tube diameter 15mm; diameter 21.3mm, wall thickness 2.75mm
Ordinary 6 tube 3 \ 4 “— tube diameter 20mm; diameter 26.8mm, wall thickness 2.75mm
Ordinary 1 inch tube 1 “— tube diameter 25.4mm; diameter 33.5mm, wall thickness 3.25mm wall thickness error +12%; – 15%, diameter deviation plus or minus 0.5mm