search
Loading...
Compression Springs Compression Springs

Enter your Outside Diameter and Free Length
Hint: For larger search results, enter a bigger range of Min and Max Inputs

Outside Diameter
to
Inside Diameter
to
Free Length
to
Wire Diameter
to
Total Coils
to
Rate
to
Material Type
Max. Load
to
Max. Deflection
to
Solid Height
to
*Required Field
Extension Springs Extension Springs

Enter your Outside Diameter and Length Inside Hook
Hint: For larger search results, enter a bigger range of Min and Max Inputs

Outside Diameter
to
Length Inside Hook
to
Wire Diameter
to
Max. Load
to
Max. Deflection
to
Initial Tension
to
Rate
to
Material Type
*Required Field
Torsion Springs Torsion Springs

Enter your Outside Diameter and Total Coils
Hint: For larger search results, enter a bigger range of Min and Max Inputs

Outside Diameter
to
Inside Diameter
to
Total Coils
to
Free Position
to
Wire Diameter
to
Body Length
to
Max. Torque
to
Max. Deflection
to
Rate
to
Leg Length
to
Material Type
*Required Field
Conical Springs Conical Springs

Enter you Small Outside Diameter, Large Outside Diameter and Free Length
Hint: For larger search results, enter a bigger range of Min and Max Inputs

Small Outside Diameter
to
Large Outside Diameter
to
Free Length
to
Rate
to
Total Coils
to
Solid Height
to
Wire Diameter
to
Material Type
*Required Field

Spring Index Explained: Design & Functionality

Definition of Spring Index

 

Spring index is the correlation between the mean diameter of a spring and the wire diameter of a spring. This proportion will determine the strength of the spring, the stress induced on the spring, and the manufacturability of the spring. On this page you will discover how to calculate your index mathematically using the spring index formula, how to use the index in spring design, how to measure a spring in order to determine index, and the most desirable range for a spring index to be in.

 

Formula For Calculating Spring Index

Index = Mean Diameter (D) / Wire Diameter (d)
Mean Diameter (D) = Outer Diameter (OD) - Wire Diameter (d)

 

Spring Index Calculation Example

  • Outer Diameter: 1.000 inches
  • Wire Diameter: 0.080 inches


Mean Diameter = 1.000 in (OD) - 0.080 inches (d)
Mean Diameter = 0.920 inches
Index = 0.920 inches (D) / 0.080 inches (d)
Index = 11.5

Large and Small IndexLarge and Small Index

Measuring Your Spring

In order to properly calculate the spring index formula you will need to know how to measure a spring. Please see the images below to see how to properly measure a compression, extension, and torsion spring. For a more detailed explanation on how to accurately measure your spring please visit our spring measurement page.

 

Using Spring Creator Calculator to Determine Index

To see how decreasing or increasing your index will effect the strength of your spring please use our Online Spring Calculators. Simply enter the dimensions you have measured using the diagrams above and hit calculate. The spring index will be in the "physical dimensions" section. Remember, to change your index you will need to manipulate the outer diameter of your spring and/or the wire diameter of your spring.

 

Manufacturability of Your Spring Based on Spring Index

The spring index on your spring is one of the first things a spring engineer will evaluate when deciding if your spring is manufacturable and what the cost will be to manufacture your spring. If you stick to the numbers below you will have lower production costs and more availability of spring makers to manufacture your spring.

 

  • Spring Index: 0 - 3.9 : Acxess Spring Cannot Manufacture
  • Spring Index = 4 - 5 : Your Spring Falls in the Difficult Category, higher cost
  • Spring Index = 6-12 : Best Manufacturing Range Lower Cost
  • Spring Index = 13 - 15: Your Spring is Just Above Good But Not Quite in The Difficult Range
  • Spring Index = 15 - 25: Spring Falls in the Difficult Category, higher cost
  • Spring Index = Above 25 : Very expensive and difficult to manufacture, tolerances are larger
How To Measure Compression Spring Index DimensionsHow To Measure Compression Spring Index Dimensions
How To Measure Extension Spring Index DimensionsHow To Measure Extension Spring Index Dimensions
How To Measure Torsion Spring Index DimensionsHow To Measure Torsion Spring Index Dimensions

Manufacturing a Tight Spring Index

 

How Small And Large Spring Index Affects Spring MakingHow Small And Large Spring Index Affects Spring Making

Spring Index <4 is Hard To Manufacturate

 

Spring Index ExamplesSpring Index Examples
How Does My Index Affect The Strength Of My Spring?

The index of your spring is in direct correlation with how strong your spring will be. If you need to INCREASE the strength of your spring, you will need to reduce the index. There are two ways to reduce the index. The first way is to INCREASE the diameter of the wire. The second way is to DECREASE the outer diameter of the spring. If you need to DECREASE the strength of your spring, you will need to enlarge the index. There are two ways to enlarge the index. The first way is to DECREASE the diameter of the wire. The second way is to INCREASE the outer diameter of the spring. Please see the chart below for further information.

 

Buying your spring...

Once you have determined what spring dimensions will work best for you Acxess Spring is here to help. We are there for our customers from prototype to production. We have the capabilities to manufacture a multitude of different springs, which can all be seen on our types of spring page. We can manufacture springs from 0.006 inch wire diameter to 1.000 inch wire diameter for most types of springs we make. To see a list of all the services Acxess Spring offers including finish options, heat treating, packaging options and more please see our services page.

Spring Index Design ChartSpring Index Design Chart