Pacific Rim

0 Items Total: €0.00

How to Measure an Extension Spring

1. Measure the spring wire diameter, preferably to 3 decimal places for accuracy using calipers.

wire diameter extension spring

2. Measure the outside diameter of the coils (this may vary slightly coil to coil). Take the average value at the central coils of the body.

extension spring outside diameter

3. Measure the body length of the spring. The body length of the spring is the portion which excludes the hooks of looped ends. If the body is open wound, then also count the number of coils.

extension spring body length

4. Measure the free length of the extension spring by measuring to the inside edge of end to end of each hook or looped end.

extension spring end to end hooks

5. Measure the loop or hook length.

extension spring hook length

6. If the outside diameter of the loop or hook is enlarged or reduced, measure the loop or hook outside diameter.

extension spring hook outside diameter

7. If the gap is important for assembly, measure the loop or hook opening. It is the distance from the end of the wire to the spring body.

extension spring hook opening

8. Note the relative position of the loops or hooks if the assembly requires alignment fit. Typical specification include:
90 degree position where the loops are twisted from each other.
In-line position where the loops are aligned in the same plane. If it is an in-line position, then note if the assembly
specifically needs the loop openings on the same or opposite sides.
Random Position where the assembly does not matter if in-line, 90 degree, or any position in between.

90 degree position loop extension spring

90 Degrees


inline extension spring



same side opening extension spring

Openings on the Same Side


opposite side opening extension spring

Opening on the Opposite Side

9. Note the winding direction of the coils. In most applications this is not important but review surrounding parts and whether they require the spring to be in a specific direction.

extension spring direction of wind

10. Determine the spring wire material type. If the wire is not attracted to a magnet, then it might be a special metal alloy that needs exact identification. If the material is unknown, then take note of any extreme operating conditions such as: very high or low temperatures, presence of corrosive materials or rapid cycling. Learn more about Materials.


Why Choose Lee Spring?

large selection of springs

25,000+ products
available, plus custom
products made to your specification.



Springs Available Now

for immediate delivery

FREE Plating

on all Music Wire Stock Springs

FREE Grinding

on all Standard Stock Compression Springs

in stock springs

Springs ready to ship


In Stock

Expert Engineering Assistance

on Stock and Custom Springs

Certificate of Compliance

on all Stock Springs and Custom Springs

Guaranteed RoHS Compliance

on all Stock Springs

engineering and customer service support

Engineering and
Customer Service teams ready to



Live Customer Service Support

at all Locations

Enhanced CAD Downloads

on Stock Springs Designs

Global Flexibility

allows Lee Spring to find solutions that meet your
geographic requirements wherever your business
takes you in the world