Extension Spring Manufacturer in Mumbai, India
An extension spring (also called a tension spring) stretches under load and pulls back to its original length. Gurudatta Trading Co. makes extension springs to your drawing or sample — from a single prototype to bulk orders — with the hook or loop you need.
What is an extension spring?
An extension spring is a close-wound helical spring with a hook or loop at each end. It resists being pulled apart and returns to its original length when the load is released. Unlike a compression spring, its coils touch at rest and are held together by initial tension, so the spring does not start to stretch until the pull exceeds that force.
Extension springs are used wherever a pulling force or a return motion is needed — trampolines, garage and sliding-gate mechanisms, balancers, machine return mechanisms, tool and fixture clamps, and agricultural and automotive linkages.
How an extension spring works
The load at any extension x is F = Fi + k × x, where Fi is the initial tension and k is the spring rate, found with the same formula as for a compression spring: k = G · d⁴ / (8 · D³ · Na). Initial tension is wound into the spring while it is coiled and is not part of the rate. Once the applied load passes Fi, the spring stretches by x = (F − Fi) ÷ k. Our extension spring formula guide has a worked example, and the extension spring calculator does the sums for you.
Extension spring end (hook) types
| End type | Description |
| Machine hook / machine loop | Formed directly from the end coil by bending it up — the most common and economical end |
| Full loop (twisted loop) | A complete loop formed from the end wire, centred on the spring axis |
| Side loop | A loop positioned off the spring axis to suit the mounting |
| Extended hook | A straight shank between the body and the hook for extra reach or clearance |
| Threaded insert or swivel hook | A separate threaded or swivelling fitting for adjustable or swivelling mounts |
Not sure which you have? Send a sample or a photo and we will identify and match it.
Design points that matter
- Hooks usually govern. The hooks often carry the highest stress, so the body is not always the limiting part. Our calculator checks body shear, hook bending and hook torsion and reports the lowest as the safe load.
- Specify length inside hooks. Give the length inside the hooks (or overall length), not only the body length.
- State the hook orientation. Say whether the hooks are in line or turned to a set angle.
- Limit the stretch. Fit a stop so the spring cannot be extended beyond its safe extension.
- Mention the environment. Outdoor, wet or chemical use points to stainless steel or a protective finish.
Materials and finishes
Extension springs are made from spring steel wire such as music wire or hard drawn wire, or from stainless steel where corrosion resistance matters. Plated or galvanised finishes are common for outdoor use. See our material comparison and finishes and coatings guide.
What to send for a quote
- Wire diameter and outside diameter
- Number of coils or body length, and the length inside the hooks
- Hook type and orientation
- Initial tension and the load required at a stated length, if known
- Material, finish and quantity
- A drawing, sample or photo — see how to measure a spring
Our extension springs
SS Silver Extension Spring
Stainless steel extension spring designed to absorb and store energy when stretched.
SS Extension Spring with Hook End
SS Extension Spring with Hook End – buy in bulk from Gurudatta Trading Co., Mumbai.…
Black and Silver Extension Spring Set
Black & Silver Mild Steel Extension Spring Set (3-pc) — precision-wound, Mumbai…
Small Extension Spring Assortment
Small Extension Spring Assortment (7-pc) — mixed sizes for repairs, prototyping &…
Extension Spring Assortment
Extension Spring Assortment (8-pc, mixed sizes) — genuine steel springs from a Mumbai…
Jumping Trampoline Springs
High-fatigue-life tension springs for trampolines.
Extension spring FAQs
What is the difference between an extension spring and a compression spring?
A compression spring is open-coiled and resists being squeezed. An extension spring is close-wound with a hook or loop at each end and resists being pulled apart.
What is initial tension in an extension spring?
Initial tension is the force that holds the coils together when the spring is at rest. The spring does not begin to stretch until the applied load exceeds it.
Why do extension springs usually fail at the hooks?
The bends where the hook meets the body concentrate stress, so overstretching or repeated cycling commonly cracks the spring there. A hook stress check is part of a good design.
Can you make an extension spring from a sample?
Yes. Send the sample or a photo with measurements and we will identify the hook type and quote a matching spring.
Do you supply trampoline springs?
Yes — see our trampoline spring buying guide and the extension spring range below.
Need springs made to your specification?
Gurudatta Trading Co. (Mumbai, since 2000, ISO 9001:2015) manufactures compression, extension and torsion springs to drawing or sample. Use the free Spring Rate Calculator or message us on WhatsApp.