Copper tube in the annealed condition. 4mm is to BS EN 12449. 6mm, 8mm and 10mm are to BS 2871: Part 1: Table W, annealed (EN 1057 soft). Suitable for water and gas installations. N.B. the diameters on this page ALWAYS refer to the outside diameter of the copper tube. Compare prices from: Wednesbury in Plumbing