# Custom Dual-Pitch Compression Springs

## Definition - Custom open wound compression springs whose coils have more or less pitch in between them on one side of the spring’s body.

Dual pitch compression springs are also known as double-rate springs, double pitch springs, and progressive rate springs. They have a non-linear force which means it isn’t constant as it is with a regular compression spring. This custom compression spring type has a progressive rate which means that the force increases after a certain amount of travel.

It only increases because the coils with less pitch, which exert less force, are the first to compress no matter where in the spring’s body they are located. This means that the weaker coils travel first and then the stronger coils begin to travel after more force is applied.

When defining the dimensions of this spring type you have:

• Wire Diameter
• Outer Diameter
• Free Length
• Pitch 1 (defines the pitch in between the coils of one of the sides of the compression spring)
• Pitch 2 (defines the pitch in between the rest of the coils)
• Number of Coils in Pitch 1
• Number of Coils in Pitch 2

Our “How to Measure Dual Pitch Springs” diagram to the right tells you just how to do this and how you must explain them at the time of getting a Instant Spring Quote.

When it comes to figuring out the total coils, you start at the second wire because that’s when it has made a full turn. Once you’ve done so, you subtract the closed coils at the ends (in these case there is two, one on each end) to calculate the number of active coils. The spaces with pitch in between them are calculated by adding 1 to the number of active coils. In this case we have FILL IN active coils so we have FILL IN spaces of pitch.