Get unique, complex parts easily. No matter your requirements, Master Spring creates hard-to-produce coil springs and wire forms.

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Let us help you create the custom wire form you need, from S-hooks and J-hooks to utility hooks and more.


We work closely with customers across a wide range of industries, helping them design and manufacture made-to-order parts.

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Why choose Master Spring? We prioritize customer-focused collaboration, modern equipment and the latest technology to make your parts per print.

Extension Spring Measurement Guide

Extension spring dimensions are defined as the measurements critical to the design of an extension spring. There are endless extension spring designs, and knowing how to find precise measurements will help you determine the best spring for your needs.

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What Is Extension Spring Initial Tension?

Initial tension is the tension wound between the coils of an extension spring. It keeps the coils closed and requires outside force before the coils open. To release initial tension, you must extend an extension spring until light shines through the coils.

Unlike a compression spring, an extension spring can have a preload at zero deflection. The amount of force an extension spring produces is an important part of its design and production, as it affects spring performance. Find out how to measure a spring’s initial tension below.

Initial Tension Formula: How to Measure Spring Tension

You can calculate initial tension of an extension spring with a simple formula:

P1 = P – R(T)

The variables in this equation represent the following:

  • P1 = Initial Tension
  • P = Load
  • R = Rate
  • T = Travel

For example, where R=10 pounds per inch, P=20 pounds and T=1.5 inches, you can find the pounds of force for your spring’s initial tension. Simply multiply 10 by 1.5 and subtract from 20 to get 5 pounds of force (5lbf).

P1 = 20 – 10 * 1.5

P1 = 20 – 10

P1 = 5lbf


To understand more about this equation and extension spring terminology, explore our glossary of spring and wire form terms.

If you need assistance calculating initial tension or learning how to measure a spring, contact us. At Master Spring, we help OEMs determine the best spring or wire form for their needs. To get started, request a free extension spring quote today, and include the following information:

  • Heights or lengths in the spring’s free position, installed position and fully-loaded position
  • Dimension of the cavity (hole) that the spring fits into
  • Dimension of the rod or mandrel the spring fits over
  • Description of the mating part
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Need a custom wire form or coil spring? We make it work. Fill out the contact form and a representative will respond within 1 business day. Please attach a PDF or CAD file with your request to quote.


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Your Team For Innovative Wire Forming

We provide solutions for complex, high-quality
wire forms and coil springs.

78 Congress Circle West, Roselle, IL 60172

P: 708.453.2570 | Contact Us

We do not stock standard springs,
we make made-to-order custom springs.