Extension Springs
Custom extension springs,
made in Thailand.
Extension springs that pull, return and tension — wound to your drawing with the hook geometry and initial tension your assembly needs, in wire from 0.08 mm to 8.0 mm.
The hook is part of the spring, not an afterthought
An extension spring carries load through its hooks, so hook form, orientation and radius matter as much as the coil body. We wind the body and form the hooks in one production flow, then test the finished part at the extension length on your drawing.
Initial tension, body length and maximum extension are reviewed together. If the hook is the weak point, we say so at RFQ rather than ship a spring that passes a load check but fails in service.
- Machine hooks, side hooks, extended hooks and custom loops
- Controlled initial tension and load at length
- Carbon spring steel and stainless steel
- Prototype and volume production on the same line
Where extension springs pull their weight
Extension springs return, retract or tension a mechanism. The hook geometry is usually set by the attachment point in the assembly, not by the spring alone.
Extension spring specifications
Current production is shown below. Hook geometry and extension limits are reviewed against the assembly drawing.
| Parameter | Capability |
|---|---|
| Wire diameter | 0.08–8.0 mm in current production. Planned expansion to 12.0 mm as new equipment is installed. |
| Materials | 65Mn, 72A, 82B, 60Si2Mn; stainless steel 301, 302, 304 and 316. |
| Hook forms | Machine hook, side hook, extended hook and custom loop to drawing. |
| Heat treatment | In-house stress relief and tempering. |
| Surface finish | Anti-rust oil, electrophoresis (E-coat), zinc plating, nickel plating, spray coating. |
| Wire tolerance | JIS wire tolerance by grade (JIS G 3521, JIS G 3522 or JIS G 4309). ASTM wire specification and SMI commercial tolerances available for US programs. |
| Load testing | Initial tension and load at the extended length specified on the drawing. |
| Dimensional inspection | 2.5D vision measurement and dimensional checks against the drawing. |
| Quality system | ISO 9001:2015 and ISO 14001:2015. |
| Samples | Prototype and pre-production samples against drawing. |
Wire diameter is inspected to the JIS tolerance of the ordered wire grade. For US programs, we can quote and inspect to the relevant ASTM wire specification and SMI commercial tolerances.
Materials and finishes
The wire grade and finish should follow the load, fatigue and corrosion exposure of the application — not a default.
65Mn · 72A · 82B · 60Si2Mn
Used for general return and tension duties where the load cycle and environment are within the grade’s capability.
301 · 302 · 304 · 316
Selected where moisture, cleaning or a corrosive environment makes a coated carbon spring unsuitable.
Oil · E-coat · zinc · nickel · spray
Anti-rust oil, electrophoresis, zinc plating, nickel plating and spray coating are available, including finishes that protect the hook and body together.
Checked at the length that matters
Load is measured at the extension length on your drawing, not at a convenient bench height. Dimensional and material checks run alongside it.
- Raw material tensile strength and metallographic structure
- Initial tension and load at specified length
- 2.5D vision measurement of body and hook dimensions
- Salt spray testing for plated and coated parts
- Fatigue testing for cycle-life validation
- Inspection records agreed at RFQ
What to send with your drawing
A complete drawing shortens the quote and removes assumptions.
- Wire diameter and material grade
- Body length and outside diameter
- Hook type, orientation and attachment point
- Initial tension or load at a specified length
- Maximum extension and operating environment
- Surface finish and annual quantity
PDF, DXF, STEP or a clear photo
Email your drawing to info@aofengspringthailand.com. We confirm the hook form, wire range, material and test plan before quoting.
Extension spring questions
Which hook forms can you produce?
Machine hooks, side hooks, extended hooks and custom loop forms to drawing. Hook orientation is set against your assembly drawing.
How is initial tension controlled?
We wind and test against the initial tension or load at length on your drawing, and agree the measurement method at RFQ.
Can you make extension springs in stainless steel?
Yes — 301, 302, 304 and 316 are available, subject to the wire diameter and hook form.
What is your current wire diameter range?
0.08–8.0 mm in current production, with a planned expansion to 12.0 mm as new equipment is installed. We confirm the range for a specific part at RFQ.
Send a drawing, get a quote
Tell us the attachment points, the load and the extension. We will confirm the hook form, wire range and test plan before quoting.
AOFENG SPRING (THAILAND) · Rayong, Thailand