What this calculator does
Flat-end extension springs use a straight section of wire rather than a loop, giving a larger contact area and more predictable initial tension. They are common in mechanisms that pull against a flat surface. The calculator checks initial tension, rate, travel and the stress at the flat end.
Inputs and outputs
Inputs
- Wire diameter and mean diameter
- Body coils and free body length
- Flat-end length
- Initial tension
- Working travel
- Material
Results
- Spring rate
- Initial tension and load at travel
- Body and end stress
- Maximum travel
- Load–deflection curve
Typical applications
- Automotive trim
- Furniture
- Appliance latches
- Display stands
- Packaging machinery
Design notes
The flat end must be clamped so it cannot rotate; a rotating flat end will wear a groove in the mating part. Specify the end length and the clamping method together, since both affect the stress at the transition.
The interactive calculator interface is currently in Chinese. Enter your values there, or send us the load, travel and space constraints and our engineers will return a checked calculation sheet in English.
Frequently asked questions
How is a flat end different from a hook?
A flat end contacts the mating part along a straight section, so the load is spread over a larger area and the end cannot straighten under load. A hook concentrates stress at a bend.
Can initial tension be controlled?
Yes, within the normal winding range. Very high initial tension requires special winding and should be discussed before the drawing is released.
What end length should I specify?
The flat section should be long enough to sit fully inside the clamp. The calculator reports the stress at the transition so the length can be balanced against the wire diameter.
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Need this spring manufactured?
Send a drawing, a sample or the parameters from this calculator. We will review manufacturability and reply with a quote and a sample lead time.