SEM screws (pre-assembled washer and screw units) are increasingly popular in applications where washers are used in combination with screws. A SEM is a permanent assembly with the washer held in place by the major diameter of the screw thread being larger than the hole of the washer.


SEMs provide many design and cost advantages:

  • Low cost and widely available
  • Simplify purchasing, scheduling and inventory
  • Increases productivity by eliminating separate, costly washer and screw handling on the line
  • ensures that the washer is not dropped, lost or forgotten
  • Ease of use with hand drivers and in automated production programs

SEMs are available in hex, phillips, torx and slotted drives in materials including brass, zinc plated steel and stainless steel.

We supply SEMs with the following washer combinations:

  • Internal tooth SEMS: Recommended when it is desirable to hide the teeth for appearance or to prevent snagging.
  • External Tooth SEMS: Preferred over the internal tooth style as the teeth provide greater torsional resistance being on the larger radius.
  • Split-Lock SEMS: Preferred over tooth lockwasher SEMS for use with hardened bearing surfaces.
  • Square-Cone SEMS: Provides a higher retained clamp load and improved compensation for thermal cycling and vibration. Can accept a high tension load and maintain spring action. The washer design makes for better control during installation, and improved tool bit life. Ideal for clamping fragile materials and for spanning large clearance holes.
  • Double washer SEMs: Commonly used in the electronics industry. Directly below the head is a helical split lockwasher; beneath the split lockwasher is a round flat washer.

To put our 30+ years of experience to use for you – call us today.