What is SLD?

Adding Value to a Spring Through Encapsulation

A Spring-Loaded Device (SLD) or Enhanced Spring is a device that adds value to a spring by encapsulating it in a body and providing a plunger tip or ball on one end—enabling accurate and repeatable end forces.

Not a bolt or a screw, a spring-loaded device should not be subjected to the same installation or fastening forces common with bolts and screws. An SLD does not have the head size of a screw or bolt and it has a (hollow) threaded or push-fit style body in order to encapsulate a spring.

Vlier highly recommends that you read the SLD Installation section before designing SLDs into your product or fixture.

Vlier spring-loaded devices fall into four main categories:

  • Standard Spring Plungers
  • Stubby Spring Plungers
  • Ball Plungers
  • Quick Release Plungers


Manufacturers choose spring-loaded devices over standard springs and self-manufactured parts for many reasons. The most common reasons are:

  • Accurate, repeatable end forces
  • Easier side loading (impossible for springs)
  • Simpler to install than standard springs
  • One subassembly replaces multiple components
  • Repeatable projection time after time
  • Minimal spring compression set