Machine screws are cylindrical fasteners used to join two items, commonly made of steel or stainless steel, and available in multiple sizes and finishes. SEMS screws, a subtype of machine screws, feature a washer-like, serrated head to maintain grip and prevent loosening. Weld-on screws, designed for welding onto surfaces, are marked by a threaded shank with a weld-nut on the end, available in a range of sizes and finishes, and typically constructed from steel or stainless steel.