1.1 ,This specification covers wrought high-strength ferritic steel butt-welding fittings of seamless and electric fusion-welded construction. Dimensions of the fittings are provided in the latest revisions of ASME B16.9 and MSS-SP-75. Butt-welding fittings differing from ASME B16.9 shall be furnished in accordance with Supplementary Requirement S58 of Specification A960/A960M. These fittings are for use in high-pressure gas and oil transmission and distribution systems.