Phillips pan head combination screw (SEMS screw) is pre-assembled as one unit: pan head screw + flat washer + spring lock washer. Washers stay attached and cannot fall off.

Flat washer distributes pressure to protect workpiece surface; spring washer provides elasticity for anti-loosening. Materials: Grade 4.8 carbon steel; A2(304)/A4(316) stainless steel optional. Surface finish: blue-white zinc, yellow zinc, black oxide, plain passivated for stainless steel. Widely used for electrical cabinets, home appliances, instruments, sheet metal and general hardware assembly.