SEMS Screws

SEMS screws are fasteners that combine a screw and a washer into a single pre-assembled unit. The term "SEMS" stands for "screw and washer assemblies," derived from the concept of pre-assembled bolts. Today, it is used more generally for bolts that include pre-assembled washers. 

The flat washer helps distribute the load, increasing clamping force, while the spring washer prevents the screws or bolts from loosening due to vibrations.