This Supplementary Code relates to B3.1.1.01- Mechanical Code Of Practice, Section 3.17 - Materials. It contains NZ Railways Mechanical Branch Code 91 B - High Tensile Steel Castings For Transition Heads to Drawing No.28148; Issue 1, which contains information relevant to the uses of high tensile steel castings for transition heads. Operators are to use those sections that are relevant to their operation.