You are looking at a stainless steel extension spring wholesale program from BQUQ, a 20-year precision manufacturing factory in Dongguan, China. These are custom extension springs, not stock items, wi
You are looking at a stainless steel extension spring wholesale program from BQUQ, a 20-year precision manufacturing factory in Dongguan, China. These are custom extension springs, not stock items, with a guaranteed tolerance of ±0.02 mm on outer diameter and ±0.5° on leg position, a maximum hardness of 48 HRC, and a standard lead time of 7 working days after drawing approval. We build them for engineers who need repeatable force over millions of cycles, and we ship worldwide with no MOQ.
Most extension spring failures come from stress relaxation, not wire breakage. We counter that by cold-winding stainless steel wire (302, 304, 316, and 17-7 PH) on CNC coiling machines with a mandrel accuracy of ±0.005 mm. Then we pre-stress each spring to 25% above its maximum working load. This sets the coils and removes initial set, so the free length changes less than 1% after 500,000 cycles at full deflection. If you need a spring that pulls a door latch 10,000 times a day, this is the difference between a 2-year life and a 10-year life.
We produce extension springs from 0.1 mm to 8.0 mm wire diameter, with free lengths from 3 mm to 300 mm. Coil count can be as low as 2 or as high as 50. Legs are custom: cross-over center loops, extended hooks, side hooks, or threaded ends. For mechanical seals and electric switches, we hold leg angle tolerance to ±2°. For heavy-duty agricultural equipment, we recommend 316 stainless for corrosion resistance in salt spray up to 1,000 hours per ASTM B117. We also offer initial tension control from 0.5 N to 200 N, measured on a digital force tester with 0.01 N resolution.
We stock four stainless grades. Type 302 is our default—it offers the best balance of tensile strength (1,200–1,500 MPa) and cost. Type 304 is for food and medical applications where weldability matters. Type 316 is for marine and chemical environments. 17-7 PH is our high-temperature choice, holding its set up to 315°C. After coiling, we stress-relieve every spring in a nitrogen-controlled furnace at 400°C for 30 minutes. This removes residual coil stress and stabilizes the microstructure. For 17-7 PH, we add a precipitation hardening cycle at 480°C for 1 hour to reach 48 HRC.
Stainless steel springs can crack if you leave micro-cracks from grinding or coiling. We shot-peen all springs above 2.0 mm wire diameter to 0.25 mm depth, which compresses the surface and increases fatigue life by 40%. Then we passivate per ASTM A967, giving a surface finish of Ra 0.4 µm. We never use acid pickling that can cause hydrogen embrittlement. Each batch is baked at 200°C for 2 hours to drive out any absorbed hydrogen. This is critical for springs under constant tension in safety-critical systems like automotive brake return mechanisms.
We do not ship a spring coil without a full inspection report. On every batch, we test 5 samples for initial tension, spring rate (N/mm), and free length using a ZwickRoell universal tester with a calibration certificate traceable to ISO 17025. We measure outer diameter, inner diameter, and wire diameter with a laser micrometer at three positions along the coil. We also check leg angle and hook alignment under a 10x optical comparator. For springs with a free length above 50 mm, we perform a 100% dimensional check using a CNC vision system that records measurements to a CSV file, which we attach to your shipping invoice.
| Spec | Range / Value | Notes |
|---|---|---|
| Wire Material | 302, 304, 316, 17-7 PH | Tensile 1200–1500 MPa |
| Wire Diameter | 0.1–8.0 mm | ±0.01 mm tolerance |
| Free Length | 3–300 mm | ±0.5 mm standard |
| Outer Diameter | 2–50 mm | ±0.02 mm tolerance |
| Coil Count | 2–50 coils | Custom per drawing |
| Hardness | 45–48 HRC | After stress relief |
| Initial Tension | 0.5–200 N | ±5% of specified value |
| Surface Finish | Ra 0.4 µm | Passivated per ASTM A967 |
| Fatigue Life | 500,000 cycles | Pre-stressed 25% above max |
| Lead Time | 7 working days | After drawing approval |
| MOQ | No MOQ | Single prototype accepted |
Most spring factories push you to order 5,000 pieces before they will touch your drawing. We do not operate that way. You can send us a drawing for a single prototype and we will run it on the same CNC coiler as a 100,000-piece order. The tolerance is identical: ±0.02 mm on OD, ±0.5° on leg position. Prototype lead time is 5 working days. If you need 50 pieces for a pilot run, we quote the same unit price as for 500 pieces, because our setup cost is fixed. This is part of our precision manufacturing philosophy: the first piece must be correct, not the hundredth.
To quote you in 12 hours, we need four numbers: wire diameter, outer diameter, free length, and number of active coils. Add the leg type (cross-over, extended hook, side loop) and the maximum working load in Newtons. If you have a 3D PDF or STEP file, even better. We use those to calculate spring rate, initial tension, and stress at full deflection. We will also flag if your design exceeds the elastic limit of stainless steel—common when engineers copy a carbon steel spring design without adjusting for modulus. If you are unsure about tolerances, read our CNC machining tolerances guide to see what is achievable on a coiling machine versus a mill.
We ship extension springs in anti-corrosion VCI paper, then vacuum seal them in poly bags. For orders above 1,000 pieces, we use partitioned cartons so coils do not tangle. Each bag has a label with your part number, batch number, and inspection report ID. International shipping is via DHL, FedEx, or UPS, with a typical transit time of 3–5 days to North America and Europe. We also offer optional statistical process control (SPC) data for every production lot, which is useful if you are doing PPAP submissions for automotive or aerospace customers.
No MOQ—we accept a single prototype order with the same tolerances and quality checks as a high-volume production run.
Yes, send us the old spring, we measure wire diameter, free length, coil count, and test the load at a given extension, then reverse-engineer it within 3 days.
We use a 100% dimensional check with a CNC vision system for free length and OD, plus a 5-piece destructive force test per batch, and we provide the full inspection report with your shipment.
We run 5,000 pieces in 7 working days after drawing approval, and we can expedite to 4 days with a 15% rush fee if your machine is down.
Send us your drawing for a firm quote within 12 hours. Email sc@bquq.com or WhatsApp +86 13713157787. If you are also selecting tooling for the rest of your production line, check our CNC cutting tool selection guide to avoid mismatched tolerances between your spring and mating parts.
| Parameter | Capability |
|---|---|
| Materials | SUS302/304/316, SWC piano wire, SWP music wire, 65Mn, phosphor bronze, beryllium copper |
| Types | Compression, extension, torsion, wire forms, battery springs, touch springs |
| Wire Diameter | 0.05 - 12.0 mm |
| Tolerance | ±0.02mm standard, ±0.01mm on request |
| Surface | Zinc plating, nickel, black oxide, passivation, shot peening |
| Machines | CNC spring coiling machines, torsion machines, wire forming machines |
| Prototype | 72 hours, no MOQ on samples |
| Inspection | Load test per batch, fatigue test data on request |
