Constant Force Springs
John Evans’ Sons is an international leader in constant force spring design and manufacturing. This includes spring assemblies, pusher springs (shelf pushers or variable force), constant tension springs, clock springs and various other constant force products.
Custom design, in-house tooling and precision manufacturing as well as a wide and varied stock spring selection, combined with our commitment to quality and on-time delivery, are our strongest selling points.
Our constant force springs and assemblies can eliminate costly and complicated motors, decreasing your device size and cost. These types of springs provide:
- Smooth, even, uniform load through entire length or travel (deflection)
- Strong force yield within small spaces
- Extensive linear range
- Small package size
- Ability to easily mount to existing hardware
Design Considerations for Constant Force Springs
There are many design factors that will affect the time and cost needed to manufacture your spring. Therefore, it’s important to work with a manufacturer like John Evans’ Sons that has the knowledge needed in the design phase.
- Mounting Methods: There are several mounting methods. Your application will determine which mounting method is best for your spring’s design.
- Material: Material will certainly affect the design and project cost. High temperatures or corrosive environments will also affect the life of a spring and the required material.
- Diameter and Load: Length, material width, thickness, and coil diameter affect the spring’s load. Increased loads can be obtained by using two or more constant force springs interwound, in tandem, or in other configurations.
All of these, plus other technical considerations, need to be discussed and specified prior to creating prototypes. Our design engineering team can help ensure calculations and configurations are exact in the design phase.
Our springs are most often used in the following industries and applications:
Not sure if constant force springs can provide the right action for your product? Contact John Evans' Sons for more information.
Spring Selection Chart
(material: T301 SS, Calculations shown are at 1.0” width, interpolate for other spring material widths)
Material Thickness | 2,500 cycles | |
Coiled Dia. | Load (lbs.) | |
0.002 | 0.15 | 1.3 |
0.003 | 0.22 | 2 |
0.004 | 0.3 | 2.6 |
0.005 | 0.36 | 3.3 |
0.006 | 0.44 | 4 |
0.008 | 0.59 | 5.2 |
0.01 | 0.73 | 6.6 |
0.012 | 0.87 | 8 |
0.014 | 1.02 | 9.3 |
0.016 | 1.16 | 10.6 |
0.018 | 1.31 | 11.9 |
0.02 | 1.46 | 13.2 |
0.022 | 1.61 | 14.5 |
0.025 | 1.81 | 16.5 |
0.028 | 2.04 | 18.5 |
0.032 | 2.26 | 20.5 |
Material Thickness | 10,000 cycles | |
Coiled Dia. | Load (lbs.) | |
0.002 | 0.17 | 1 |
0.003 | 0.25 | 1.5 |
0.004 | 0.34 | 2 |
0.005 | 0.43 | 2.5 |
0.006 | 0.51 | 3 |
0.008 | 0.69 | 4 |
0.01 | 0.86 | 5 |
0.012 | 1.03 | 6 |
0.014 | 1.2 | 7 |
0.016 | 1.37 | 8 |
0.018 | 1.54 | 9 |
0.02 | 1.71 | 10 |
0.022 | 1.89 | 11 |
0.025 | 2.14 | 12.5 |
0.028 | 2.4 | 14 |
0.032 | 2.65 | 15.5 |
Material Thickness | 20,000 cycles | |
Coiled Dia. | Load (lbs.) | |
0.002 | 0.22 | 0.65 |
0.003 | 0.32 | 1 |
0.004 | 0.44 | 1.3 |
0.005 | 0.55 | 1.6 |
0.006 | 0.65 | 2 |
0.008 | 0.87 | 2.6 |
0.01 | 1.08 | 3.3 |
0.012 | 1.3 | 4 |
0.014 | 1.52 | 4.6 |
0.016 | 1.73 | 5.3 |
0.018 | 1.96 | 5.9 |
0.02 | 2.18 | 6.6 |
0.022 | 2.37 | 7.2 |
0.025 | 2.72 | 8.2 |
0.028 | 3.04 | 9.5 |
0.032 | 3.36 | 10.2 |
Material Thickness | 75,000 cycles | |
Coiled Dia. | Load (lbs.) | |
0.002 | 0.33 | 0.32 |
0.003 | 0.48 | 0.5 |
0.004 | 0.65 | 0.65 |
0.005 | 0.81 | 0.8 |
0.006 | 0.95 | 1 |
0.008 | 1.28 | 1.3 |
0.01 | 1.59 | 1.6 |
0.012 | 1.91 | 2 |
0.014 | 2.22 | 2.3 |
0.016 | 2.53 | 2.7 |
0.018 | 2.85 | 3 |
0.02 | 3.2 | 3.3 |
0.022 | 3.48 | 3.6 |
0.025 | 4 | 4.1 |
0.028 | 4.48 | 4.6 |
0.032 | 4.94 | 5.1 |
Material Thickness | 150,000 cycles | |
Coiled Dia. | Load (lbs.) | |
0.002 | 0.44 | 0.17 |
0.003 | 0.66 | 0.26 |
0.004 | 0.89 | 0.35 |
0.005 | 1.11 | 0.44 |
0.006 | 1.33 | 0.52 |
0.008 | 1.78 | 0.7 |
0.01 | 2.22 | 0.87 |
0.012 | 2.67 | 1.04 |
0.014 | 3.07 | 1.2 |
0.016 | 3.6 | 1.4 |
0.018 | 4 | 1.56 |
0.02 | 4.44 | 1.74 |
0.022 | 4.89 | 1.91 |
0.025 | 5.55 | 2.18 |
0.028 | 6.23 | 2.44 |
0.032 | 6.9 | 2.7 |

Selection Charts for the Ideal Constant Force Spring
Part Number | Load | Max Work Deflection | Band Length | Fatigue Life (cycles) | Width | Free I. D. | Thickness |
---|---|---|---|---|---|---|---|
A 3X50-SL04D16 | 0.23 | 12" | 16" | 20,000 | 0.25" | 0.516 | 0.004 |
A 3X50-SK04D15 | 0.32 | 12" | 15" | 13,000 | 0.25" | 0.438 | 0.004 |
A 3X50-SL05E17 | 0.36 | 12" | 17" | 20,000 | 0.3125" | 0.656 | 0.005 |
A 3X50-SH03C10 | 0.37 | 8" | 10" | 2,500 | 0.1875" | 0.219 | 0.003 |
A 3X50-SK04E15 | 0.4 | 12" | 15" | 13,000 | 0.3125" | 0.438 | 0.004 |
A 3X50-SL05F30 | 0.43 | 25" | 30" | 20,000 | 0.375" | 1.0 | 0.005 |
A 3X50-SH04C14 | 0.49 | 12" | 14" | 2,500 | 0.1875" | 0.297 | 0.004 |
A 3X50-SK05E16 | 0.49 | 12" | 16" | 13,000 | 0.3125" | 0.563 | 0.005 |
A 3X50-SL06F24 | 0.52 | 18" | 24" | 20,000 | 0.375" | 0.781 | 0.006 |
A 3X50-SH04D14 | 0.66 | 12" | 14" | 2,500 | 0.25" | 0.297 | 0.004 |
A 3X50-SL06G24 | 0.7 | 18" | 24" | 20,000 | 0.5" | 0.781 | 0.006 |
A 3X50-SK06F23 | 0.71 | 18" | 23" | 13,000 | 0.375" | 0.672 | 0.006 |
A 3X50-SH04E14 | 0.83 | 12" | 14" | 2,500 | 0.3125" | 0.297 | 0.004 |
A 3X50-SL08G31 | 0.93 | 24" | 31" | 20,000 | 0.5" | 1.047 | 0.008 |
A 3X50-SK06G23 | 0.95 | 18" | 23" | 13,000 | 0.5" | 0.672 | 0.006 |
A 3X50-SH05E15 | 1.03 | 12" | 15" | 2,500 | 0.3125" | 0.359 | 0.005 |
A 3X50-SK08G30 | 1.26 | 24" | 30" | 13,000 | 0.5" | 0.875 | 0.008 |
A 3X50-SL10J33 | 1.46 | 24" | 33" | 20,000 | 0.625" | 1.328 | 0.010 |
A 3X50-SH06F21 | 1.48 | 18" | 21" | 2,500 | 0.375" | 0.438 | 0.006 |
A 3X50-SK08J30 | 1.58 | 24" | 30" | 13,000 | 0.625" | 0.875 | 0.008 |
A 3X50-SH06G21 | 1.97 | 18" | 21" | 2,500 | 0.5" | 0.438 | 0.006 |
A 3X50-SK10J32 | 1.98 | 24" | 32" | 13,000 | 0.625" | 1.109 | 0.010 |
A 3X50-SL12K42 | 2.09 | 30" | 42" | 20,000 | 0.75" | 1.578 | 0.012 |
A 3X50-SK10K32 | 2.37 | 24" | 32" | 13,000 | 0.75" | 1.109 | 0.010 |
A 3X50-SH08G28 | 2.63 | 24" | 28" | 2,500 | 0.5" | 0.578 | 0.008 |
A 3X50-SL12P42 | 2.8 | 30" | 42" | 20,000 | 1" | 1.578 | 0.012 |
A 3X50-SK12K40 | 2.84 | 30" | 40" | 13,000 | 0.75" | 1.344 | 0.012 |
A 3X50-SH08J28 | 3.29 | 24" | 28" | 2,500 | 0.625" | 0.578 | 0.008 |
A 3X50-SL15P46 | 3.5 | 30" | 46" | 20,000 | 1" | 1.984 | 0.015 |
A 3X50-SK12P40 | 3.79 | 30" | 40" | 13,000 | 1" | 1.344 | 0.012 |
A 3X50-SH10J29 | 4.12 | 24" | 29" | 2,500 | 0.625" | 0.734 | 0.010 |
A 3X50-SL15R46 | 4.37 | 30" | 46" | 20,000 | 1.25" | 1.984 | 0.015 |
A 3X50-SK15P42 | 4.74 | 30" | 42" | 13,000 | 1.0" | 1.672 | 0.015 |
A 3X50-SH10K29 | 4.95 | 24" | 29" | 2,500 | 0.75" | 0.734 | 0.010 |
A 3X50-SK18P47 | 5.69 | 32" | 47" | 13,000 | 1.0" | 2.0 | 0.018 |
A 3X50-SL20R54 | 5.83 | 36" | 54" | 20,000 | 1.25" | 2.625 | 0.020 |
A 3X50-SH12K36 | 5.94 | 30" | 36" | 2,500 | 0.75" | 0.875 | 0.012 |
A 3X50-SL20S54 | 6.99 | 36" | 54" | 20,000 | 1.5" | 2.625 | 0.020 |
A 3X50-SH12P36 | 7.92 | 30" | 36" | 2,500 | 1.0" | 0.875 | 0.012 |
A 3X50-SL25S59 | 8.74 | 36" | 59" | 20,000 | 1.5" | 3.297 | 0.025 |
A 3X50-SK20S52 | 9.48 | 36" | 52" | 13,000 | 1.5" | 2.219 | 0.020 |
A 3X50-SH16P38 | 10.6 | 30" | 38" | 2,500 | 1.0" | 1.156 | 0.016 |
A 3X50-SL25U59 | 11.7 | 36" | 59" | 20,000 | 2.0" | 3.297 | 0.025 |
A 3X50-SK25S57 | 11.9 | 36" | 57" | 13,000 | 1.5" | 2.781 | 0.020 |
A 3X50-SL31U69 | 14.4 | 42" | 69" | 20,000 | 2.0" | 4.078 | 0.031 |
A 3X50-SK25U57 | 15.8 | 36" | 57" | 13,000 | 2.0" | 2.781 | 0.025 |
A 3X50-SH20R47 | 16.5 | 36" | 47" | 2,500 | 1.25" | 1.469 | 0.020 |
A 3X50-SK31U68 | 19.6 | 42" | 68" | 13,000 | 2.0" | 3.438 | 0.031 |
A 3X50-SH20S47 | 19.8 | 36" | 47" | 2,500 | 1.5" | 1.469 | 0.020 |
A 3X50-SH25S48 | 24.8 | 36" | 48" | 2,500 | 1.5" | 1.828 | 0.025 |
A 3X50-SH25U48 | 33 | 36" | 48" | 2,500 | 2.0" | 1.828 | 0.025 |
A 3X50-SH31U58 | 40.9 | 42" | 58" | 2,500 | 2.0" | 2.266 | 0.031 |
Available from our distributor, Stock Drive Products. Tel: 516-328-3300
Material Thickness | 2,500 cycles | 10,000 cycles | 20,000 cycles | 75,000 cycles | 150,000 cycles | |||||
---|---|---|---|---|---|---|---|---|---|---|
Coiled Dia. | Load | Coiled Dia. | Load | Coiled Dia. | Load | Coiled Dia. | Load | Coiled Dia. | Load | |
0.002 | 0.15 | 1.3 | 0.17 | 1.0 | 0.22 | 0.65 | 0.33 | 0.32 | 0.44 | 0.17 |
0.003 | 0.22 | 2.0 | 0.25 | 1.5 | 0.32 | 1.0 | 0.48 | 0.50 | 0.66 | 0.26 |
0.004 | 0.30 | 2.6 | 0.34 | 2.0 | 0.44 | 1.3 | 0.65 | 0.65 | 0.89 | 0.35 |
0.005 | 0.36 | 3.3 | 0.43 | 2.5 | 0.55 | 1.6 | 0.81 | 0.80 | 1.11 | 0.44 |
0.006 | 0.44 | 4.0 | 0.51 | 3.0 | 0.65 | 2.0 | 0.95 | 1.00 | 1.33 | 0.52 |
0.008 | 0.59 | 5.2 | 0.69 | 4.0 | 0.87 | 2.6 | 1.28 | 1.30 | 1.78 | 0.70 |
0.010 | 0.73 | 6.6 | 0.86 | 5.0 | 1.08 | 3.3 | 1.59 | 1.60 | 2.22 | 0.87 |
0.012 | 0.87 | 8.0 | 1.03 | 6.0 | 1.30 | 4.0 | 1.91 | 2.00 | 2.67 | 1.04 |
0.014 | 1.02 | 9.3 | 1.20 | 7.0 | 1.52 | 4.6 | 2.22 | 2.30 | 3.07 | 1.20 |
0.016 | 1.16 | 10.6 | 1.37 | 8.0 | 1.73 | 5.3 | 2.53 | 2.70 | 3.60 | 1.40 |
0.018 | 1.31 | 11.9 | 1.54 | 9.0 | 1.96 | 5.9 | 2.85 | 3.00 | 4.00 | 1.56 |
0.020 | 1.46 | 13.2 | 1.71 | 10.0 | 2.18 | 6.6 | 3.20 | 3.30 | 4.44 | 1.74 |
0.022 | 1.61 | 14.5 | 1.89 | 11.0 | 2.37 | 7.2 | 3.48 | 3.60 | 4.89 | 1.91 |
0.025 | 1.81 | 16.5 | 2.14 | 12.5 | 2.72 | 8.2 | 4.00 | 4.10 | 5.55 | 2.18 |
0.028 | 2.04 | 18.5 | 2.40 | 14.0 | 3.04 | 9.5 | 4.48 | 4.60 | 6.23 | 2.44 |
0.031 | 2.26 | 20.5 | 2.65 | 15.5 | 3.36 | 10.2 | 4.94 | 5.10 | 6.90 | 2.70 |

CLICK for a larger selection chart, LIVE data & ordering links!
STOCK Constant Force Spring Selection Chart
Order small quantities (click chart shown above).