What This Tension Spring Does and Why Tolerance Matters This is a custom Tension Spring built for exact force control in mechanical assemblies. You get a load accuracy of ±3% across the full deflectio
This is a custom Tension Spring built for exact force control in mechanical assemblies. You get a load accuracy of ±3% across the full deflection range, with an outer diameter tolerance of ±0.02 mm and a free length tolerance of ±0.05 mm. We hold wire diameter to ±0.01 mm, which directly stabilizes your spring rate. Lead time is 7 days for prototypes and 15 days for production runs, and we ship from our Dongguan factory with a hardness range of 45–52 HRC after heat treatment. No MOQ—order one piece or one million.
We keep 12 wire grades in-house so your Tension Spring doesn't wait on raw material. For general use, we use music wire ASTM A228 (0.2–6.0 mm diameter) and hard-drawn steel A227. For corrosive or high-temp environments, we offer stainless steel 302 (A313) and 316 (A478). For high-fatigue applications like valve return mechanisms, we use chrome silicon A401 and chrome vanadium A231. Each coil is wound on a CNC former with a pitch accuracy of ±0.03 mm, which keeps your load curve linear within 1% of calculated values.
We stress-relieve every Tension Spring at 250–300°C for 30 minutes after coiling. This removes residual stress from the wire drawing process and raises the elastic limit by 15%. For high-cycle applications, we add shot peening (intensity 0.2–0.4 mmA) to compress the surface layer, increasing fatigue life by 200% compared to unpeened springs. Standard surface finish is Ra 0.8 µm, but we can achieve Ra 0.4 µm with a micro-polish pass. If your spring needs corrosion resistance, we apply zinc plating (8–12 µm) or electroless nickel (25 µm) per ASTM B633.
Your Tension Spring fails first at the hooks, so we machine them with the same precision as the coils. We offer six hook styles: full loop, half loop, extended hook, cross-over center loop, double torsion, and reduced OD hook. Each hook is formed on a dedicated mandrel to hold the inside diameter to ±0.03 mm. We inspect hook alignment with a vision system that checks angular deviation to ±1.5 degrees. For dynamic loads, we add a stress-relief notch at the hook bend to eliminate crack initiation points—this is standard, not an extra-cost option.
Every Tension Spring we ship passes a load test at 25%, 50%, and 75% of maximum deflection. We use a digital force gauge with an accuracy of ±0.5% of reading, and we record the actual load curve on a certificate of conformance. Free length and outer diameter are checked on a CNC optical comparator with a resolution of 0.001 mm. We also perform a 10-cycle compression set test on each batch to confirm the spring returns to within 0.2% of its original free length. If any unit fails, the entire batch is stopped and re-sorted.
We pack Tension Springs in anti-static VCI (vapor corrosion inhibitor) bags, then place them in double-wall cartons with dividers to prevent interlocking. For springs over 50 mm free length, we use individual tubes to avoid tangling. Each carton is labeled with your part number, lot number, and heat treatment batch. We have shipped to 34 countries without a single corrosion complaint since 2018. For express shipments, we use vacuum-sealed bags with desiccant packs rated for 60 days of humidity protection.
Prototype Tension Springs (1–50 pieces) ship in 7 days from drawing approval. Production runs (50–10,000 pieces) ship in 15 days. For orders above 10,000 pieces, add 5 days for wire spool changes and additional QC sampling. MOQ is zero—we accept a single prototype spring. Tooling cost is $0 for standard wire diameters (0.2–6.0 mm). For non-standard wire, we charge a $150 setup fee, which is waived for orders above 2,000 pieces. We provide free DFM feedback within 24 hours of receiving your drawing, including spring rate calculations and hook stress analysis.
| Parameter | Specification |
|---|---|
| Wire diameter range | 0.2 mm – 6.0 mm |
| Materials | ASTM A228, A227, A313, A478, A401, A231 |
| Free length tolerance | ±0.05 mm (up to 100 mm length) |
| Outer diameter tolerance | ±0.02 mm |
| Hardness (after heat treatment) | 45–52 HRC |
| Surface finish (Ra) | 0.8 µm standard, 0.4 µm optional |
| Load accuracy | ±3% at specified deflection |
| Hook angular deviation | ±1.5 degrees |
| Fatigue life (shot peened) | 10^6 cycles at 50% max load |
| Lead time (prototype / production) | 7 days / 15 days |
| MOQ | No MOQ (1 piece accepted) |
Your Tension Spring is often the last mechanical component to be specified, but it interacts directly with your machined parts. If your spring seat has a tight bore tolerance, check our CNC machining tolerances guide to confirm your hole tolerances align with our spring OD tolerance of ±0.02 mm. For springs that sit on a threaded stud or a turned shaft, the surface finish of your mating part affects friction and spring seating—our CNC cutting tool selection guide covers how to achieve Ra 0.4 µm on those surfaces. We also manufacture the mating components (CNC-machined spring seats, retaining washers, and stamped hooks) in the same factory, so you can order a complete sub-assembly with a single drawing—saving you a separate supplier audit.
We have no MOQ—you can order a single prototype spring to validate your design, and production pricing kicks in at 50 pieces.
Yes, send us a sample and we will reverse-engineer the wire diameter, coil count, and free length using a force-displacement curve tracer, then replicate the load curve within ±2%.
We perform in-process SPC (statistical process control) on every 50-piece batch, checking OD, free length, and load at 3 points, and we provide a full inspection report with each shipment.
For standard wire diameters in stock, we can ship a 100-piece prototype in 72 hours using express machining and overnight heat treatment, but this requires drawing approval by 10 AM CST.
Send us your Tension Spring drawing, a sketch, or a sample part. Our engineers will respond within 12 hours with a firm quote, including wire material recommendation, load curve calculation, and a DFM note on hook geometry. We are a precision manufacturing factory in Dongguan, China, with 20 years of CNC machining, stamping, and spring-making experience. No MOQ, no tooling fee for standard wire, and we speak English—no translation delays. Email your drawing to sc@bquq.com or message us on WhatsApp at +86 13713157787. We will also run a free stress analysis for your hook design to prevent early failure. Send your drawing now and get a price that competes with local suppliers while holding ±0.02 mm tolerance.
| 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 |
