SEMS Screws are a special type fastener that always includes a washer. The word SEMS is derived from the word assemblies, or asSEMblies.
The reason is when manufacturing SEMS Screws, washers are added between the heading process to the thread forming process.
Unlike most of its counterparts, having a washer already placed onto the screw will greatly reduce time and cost for manufactures.
Usually, placing the washer onto the screw will require labor cost and time because some can only be done by hand.
Another reason how SEMS Screws are different is that the washers utilized in the assembly have a smaller internal diameter, because the threads are not processed yet.
Most SEMS Screws are created as Machine Screws.
It is common for SEMS Screws to come with one or two pieces of washer, depending on the size and requirement.
Sometimes Spring Lock, Flat, External Tooth or Internal Tooth Washers are used in the assembly. SEMS Screws are made with carbon steel or stainless steel.
Mostly SEMS Screws are coated with zinc or yellow zinc to help resist corrosion.