Butt weld fittings would also be referred to as welded pipe fittings. When these would be used in stainless steel and carbon steel, they would be able to offer certain advantages as compared to socket weld and threaded fittings. Whereas socket weld would only be available up to a specific size, you would find butt weld fittings to be available in sizes starting 1/2 inch to 72 inch.