Spring Index

The spring index is the relationship between the mean diameter and wire diameter. The equation is shown below. This is a very important relationship to consider for manufacturing ease and cost control. As a general rule the index should be above 3 and less than 20. Springs designed outside these limits increase cost and require more tolerance.

Springs with small indexes increase tooling wear and are more likely to require additional processing steps to ensure adequate life. Large index springs often require additional tolerance on both diameter and length.

where I= index, D= Mean Coil Diameter, d=Wire Diameter

Please contact the Newcomb Spring facility nearest you for more information on spring index and other considerations of spring design. Newcomb Spring also offers a special technical guide on CD that includes an animated glossary and information on spring characteristics. To request one of our technical cds, visit our Quick Contact page (please write that you are requesting a CD in the Notes field).