In the case of butt welding pipe and/or fitting having unequal wall thickness, of which the difference is more than 3 mm in outer surface and/or 1.5 mm in inner surface, the end of the thicker pipe shall be trimmed by grinding as per the Fig 3.4.1 (a) , (b) and © shown below. The gradient of this trimming shall be less than 300 between worked and un-worked parts shown as below.