API Specified 6B Weld Neck Flanges have restricted bores to match standard pipe sizes and schedules. API spec 6A specified, 6 Bx Weld Neck Flanges, have material and dimensions that conform to the requirement for full bore integral flanges. Weld Neck Flanges provide dimensions of specific portions of the flange, with tolerance that is added together along with an undefined weld bevel, to achieve a length. Customers may specify Weld Neck length if required.