Free length

Where it comes up

• Springs, wire forms, and fourslideCompression, extension, and torsion springs, wire forms, and fourslide clips made from round wire and flat strip.

Related terms

Spring rate

Spring rate is the load needed to deflect a spring one unit of distance, expressed in lb/in or N/mm. It depends on wire diameter, coil diameter, active coils, and material. On commercial-grade compression springs, load at a set height is typically held to about ±10%.

Solid height

Solid height is the length of a compression spring when it is compressed until all coils touch. A design should never drive a spring to solid in service, and most designs keep maximum working deflection to about 80–85% of the travel available before solid height.