Extension Spring Measurements - How to Measure an Extension Spring

diagram showing how to measure an extension spring

To measure your extension spring, you'll need to focus on the following dimensions:

  • Outer Diameter
  • Length Inside Hook
  • Wire Diameter
  • Inner Diameter

Please see graphic to the right for more help.

Springs are accurately measured with a dial caliper. The reason for this is because a caliper provides you with a more exact measurement. Wondering why this is so important? Well, take your spring's wire diameter as an example. In most cases, if the spring's wire diameter is off by 0.001" it'll affect your spring's rate and travel so one must have exact measurements when measuring a spring.

Another thing one must focus on when it comes to their spring design is the spring's hook types. The hook types available are the following:

Machine Hooks These hooks are made from the last coils being bent out to form the hooks.

extension spring with machine hook

Cross-over Center Hooks These hooks are made from the last coils of the spring as well but these bend out the full coil and then bend the bottom wire of the hook to to the center of the spring.

extension sprong with cross-over-center hook

Side Hooks These hooks are the simplest hooks to create on a spring because the last coil is simply bent out from the end of the coil.

extension spring with side hook

Extended Hooks These hooks are great for when the previously listed hooks don't work when being installed. (You may also have an extension spring with no hooks.

extension spring with extended hook