ITW Shakeproof industrial


The SEMS preassembled screw and washer is another ITW Shakeproof Industrial invention.

We offer many combinations of tooth lock washers, helical spring lock washers, and conical washers preassembled to machine screws, thread forming, thread cutting, and self-drilling screws. For you specific preassembled needs, please contact us at

SEMS External Tooth

SEMS – External Tooth Lock-Washer:

  • For use when the surface area can be marred
  • Absorbs assembly torque
SEMS Helical

SEMS – Helical Lock Washer:

  • Meets ASTM specifications
  • Provides resistance to loosening
  • Available in all lock-washer styles
SEMS Dished

SEMS – Dished:

  • Allows for more force on soft or thin materials
  • Internal teeth lock into the bolt to prevent back off
  • Helps prevent damage to the surface area
SEMS Conical

SEMS – Conical:

  • Doesn’t disturb the surface area
  • Adds spring tension to the joint
  • Distributes load over a wider area
SEMS Square Cone

SEMS – Square Cone®:

This unique Sems fastener features an integral, free-spinning, Square Cone washer.With two distinct configurations, this dual action spring washer has two separate load deflection rates. The configurations act in unison to provide a reliable low-torque, controlled-tension fastener. The Square Cone Sems assembly provides a higher retained clamp load and improved compensation for thermal cycling and vibration. This fastener is capable of accepting a high tension load while maintaining a live spring action and generates a constant load, even with variations in installation torques. By increasing the acceptable driving torque range, it enhances flexibility in component design.

The Square Cone washer’s long deflection period and two-stage loading contribute to better control during installation, improve tool bit life and reduce operator fatigue. Load is directed toward the outer diameter of the washer, making the fastener ideal for clamping fragile materials and for spanning large clearance holes.