A stud with threads on both ends, no head. It is inserted into the threaded hole of one component, then fitted with nuts to connect two workpieces. Made of carbon steel and alloy steel, available in strength grades 4.8, 8.8, 10.9, 12.9. Surface treated with black oxide, forming a black protective film. Suitable for indoor environments with low anti-corrosion requirements. Widely used in machinery, pressure vessels, molds, pipeline flange connections.