Stainless Steel Extension Tension Springs Collection 02 is a ready-to-quote family of custom extension springs built for engineers who need predictable force, precise free length,
Stainless Steel Extension Tension Springs Collection 02 is a ready-to-quote family of custom extension springs built for engineers who need predictable force, precise free length, and corrosion resist
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Stainless Steel Extension Tension Springs Collection 02 is a ready-to-quote family of custom extension springs built for engineers who need predictable force, precise free length, and corrosion resistance. We hold wire diameter tolerance to ±0.02 mm, coil OD to ±0.05 mm, and free length to ±0.10 mm over 20 mm, with a consistent hardness of 42–48 HRC and surface finish at Ra 0.8. Typical lead time for prototypes is 7 days, and production runs ship in 15 days from drawing approval.
How We Control Load Accuracy on Your Extension Springs
Load deviation is the killer in tension spring design. Our CNC coiling machines run with a closed-loop wire feed encoder, holding rate accuracy to ±3% of specified initial tension and ±5% of the full spring rate. For Collection 02, we measure initial tension on every tenth piece using a calibrated digital force gauge, and we adjust the coiling parameters live if the mean drifts more than 1 N. This gives you consistent force across batches, not just within one box.
Materials and Heat Treatment We Use for Collection 02
We start with either SUS302 (1.4310) or SUS316L (1.4404) stainless steel wire, depending on whether you need higher tensile strength or better chemical resistance. SUS302 is cold drawn to a tensile range of 1600–1850 MPa, then stress relieved at 400 °C for 20 minutes to set the coil shape without losing spring temper. SUS316L is solution annealed before coiling, then age hardened to 42 HRC minimum, giving you pitting resistance equal to the base alloy. No plating, no coating — the surface is passivated to ASTM A967.
End Configurations and Hook Options That Fit Real Assemblies
Collection 02 includes five standard end forms: full loops, extended hooks, cross-over center loops, side hooks, and threaded inserts. For extended hooks, we control the angle to ±2° and the hook length to ±0.15 mm. If you have a rotating assembly, we can add a swivel loop option that reduces fatigue at the hook transition. We also offer a closed-and-ground end for high-cycle applications where the hook radius is the first failure point.
Inspection Before Every Shipment: What We Measure
Every lot of Stainless Steel Extension Tension Springs Collection 02 goes through a 4-step check. First, we verify free length and OD on a Nikon Vision measuring machine with 0.001 mm resolution. Second, we test load at 20%, 50%, and 80% of maximum deflection using a 500 N load cell with 0.1% accuracy. Third, we check surface finish with a portable profilometer on three coils per batch. Fourth, we do a 100% visual inspection for cracks, scratches, or rust spots under 5x magnification. Only after all four pass do we pack for shipment.
Surface Finish Options and Passivation for Harsh Environments
Standard finish is Ra 0.8 as-coiled, which suits most indoor mechanical assemblies. If your application sees salt spray, washdown, or acidic fumes, we offer electropolishing to Ra 0.4 and a citric acid passivation step that removes free iron from the surface. For food-grade or pharmaceutical lines, we can also add a final ultrasonic cleaning and individual bagging in class 1000 cleanroom conditions. Tell us the environment; we will select the finish that keeps your spring alive longer than the rest of the machine.
Lead Time and Prototype Logic for Custom Tension Springs
Because Collection 02 uses standard wire diameters from 0.5 mm to 8.0 mm, we keep raw material stock for SUS302 and SUS316L in our Dongguan warehouse. Prototypes go to CNC coiling within 24 hours of drawing approval, and you have parts in hand by day 7. For production orders above 500 pieces, we run multiple cavities in parallel, so your 50,000-piece order ships in 15 days. We will never quote you a 4-week lead time for a simple extension spring — if we cannot do it faster, we will tell you straight.
Load Testing Data We Share With Every Batch
You do not need to guess whether your spring matches the drawing. Each shipment includes a printed load-test report with the actual measured values for free length, OD, wire diameter, load at specified deflections, and initial tension. We also include a Cpk value for each dimension, calculated from a sample of 32 parts per lot. If your quality team requires a PPAP Level 3, we can provide the full package, including FMEA and control plan, with a 3-day add-on to the lead time.
Parameter
Specification Range
Notes
Wire diameter
0.5 – 8.0 mm
SUS302 or SUS316L, cold drawn
Free length
5 – 300 mm
Tolerance ±0.10 mm for lengths >20 mm
Coil outer diameter
3 – 60 mm
Tolerance ±0.05 mm
Hardness
42 – 48 HRC
After stress relief or age hardening
Initial tension
0.5 – 50 N
±3% of specified value
Spring rate
0.1 – 100 N/mm
±5% at 50% deflection
Surface finish Ra
0.8 μm as-coiled
0.4 μm available with electropolish
Runout (coil alignment)
≤0.3 mm total
Measured on 10x free length
Operating temperature
-40 °C to +250 °C
Higher temp reduces load capacity
Lead time
7 days prototype / 15 days production
From drawing approval
MOQ
No MOQ
Order 1 piece or 100,000
What is the minimum order quantity for Collection 02?
Zero — we accept a single prototype piece for testing, and pricing scales down gradually as volume increases, with no MOQ ever required.
Can you customize hook length or coil diameter beyond the standard table?
Yes, any dimension in the table can be adjusted to your drawing, and we will recalculate the spring rate and initial tension to match your load requirement.
How do you guarantee quality for a small batch of 10 pieces?
We run the same inspection protocol for 10 pieces as for 10,000 — every piece is measured for free length and OD, and load is verified on all pieces if the batch is under 50.
What is the fastest lead time if I need parts in 3 days?
For wire diameters under 3.0 mm and simple loop ends, we can do a 3-day express prototype service at a 20% surcharge, but we will only offer this if the geometry is truly simple.
For material selection and wire diameter choices, read our CNC cutting tool selection guide to understand how spring wire interacts with your machining process. If you are mating these springs into a precision assembly, check the CNC machining tolerances guide to match the spring tolerances with your housing dimensions.
Send us your drawing for Stainless Steel Extension Tension Springs Collection 02 and get a firm quote within 12 hours — no hidden tooling fees, no minimum quantity. Email sc@bquq.com or WhatsApp +86 13713157787 with your PDF, STEP, or DXF file. We will reply with a full technical review, load calculations, and a delivery date you can plan around.
