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SEMS screws are pre-assembled fastener units combining a machine screw or tapping screw with one or more free-spinning washers. The washer is fitted onto the blank before thread rolling, permanently locking it under the head to prevent loss while allowing independent rotation during fastening.
Pre-assembled combination screws eliminate manual washer placement, significantly speeding up assembly line production, reducing labor costs, preventing missing washers, and ensuring consistent clamping force across high-volume fastening operations.
SEMS screws can be configured with various washer types depending on application needs, including flat washers for load distribution, split spring lock washers to resist vibration loosening, external/internal tooth lock washers for grounding, and dual-washer assemblies.
They are typically manufactured from carbon steel, alloy steel, or stainless steel (SUS304, SUS316). Common surface finishes include clear zinc plating, yellow zinc, black oxide, nickel plating, and anti-corrosion coatings to withstand harsh environments.
Yes, SEMS screws can be removed and reused just like standard screws. Because the washer remains captive on the screw shank, maintenance and field servicing are simplified without risk of dropping or misplacing small hardware components.
They are widely utilized in automotive manufacturing, electrical equipment, consumer electronics, telecommunications, household appliances, and industrial machinery where rapid assembly and anti-vibration reliability are critical.
