Aug 28, 2018

Helical extension springs exert a force by pulling or stretching them.  Usually, they are made from round wire and are close-wound with the initial tension between the coils.  Their ends can be formed with loops in many varieties to attach to their applications. [caption id="attachment_1378" align="aligncenter" width="444"]Extension Springs .040 Zin plated music wire extension for marine products Extension Springs .040 Zin plated music wire extension for marine products[/caption] Material data sheet:

Common Spring Materials

Max Recommended % Tensile

St

Sb

Music Wire

45

75

Chrome Silicon

45

75
Chrome Vanadium

45

75

302 Stainless Steel

35

55

316 Stainless Steel

35

55

17-7 Stainless Steel

45

75
The following tables give tolerances that can be used as a reference.  Actual manufacturing tolerances will depend on the spring specifics.  

Outside Diameter Tolerances:

Wire Diameter (in)

Spring Index, D/d

4

6

      8            10           12

14

16

0.015

 0.002 0.002 0.003 0.004 0.005 0.006 0.007

0.023

 0.002 0.003 0.004 0.006 0.007 0.008

0.01

0.035

 0.002 0.004 0.006 0.007 0.009 0.011 0.013

0.051

 0.003 0.005 0.007

0.01

 0.012 0.015 0.017

0.076

 0.004 0.007

0.01

 0.013 0.016 0.019 0.022

0.114

 0.006 0.009 0.013 0.018 0.021 0.025 0.029

0.171

 0.008 0.012 0.017 0.023 0.028 0.033 0.038

0.25

 0.011 0.015 0.021 0.028 0.035 0.042 0.049

0.375

 0.016

0.02

 0.026 0.037 0.046 0.054 0.064

0.5

 0.021

0.03

0.04

 0.062

0.08

0.1

 0.125
 

Spring Free Length Tolerances

.5 in or less

0.02

0.5" to 1.0"

0.03

1" to 2.0"

0.04

2" to 4"

0.06

4" to 8"

0.093

8" to 16"

0.156

16" to 24"

0.218

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