A bearing is a component you cannot inspect by looking at it. This page sets out exactly what is checked at each stage, the equipment used, the sampling plan, and the documents that travel with the goods.
| Inspection stages | Pre-production · in-process · final |
|---|---|
| Sampling standard | ISO 2859-1, AQL 1.0 normal inspection (unless specified) |
| Dimensional check | Boundary dimensions, bore/OD/width, runout, clearance |
| Functional check | Rotation torque, noise/vibration, grease fill weight |
| Material documents | EN 10204 3.1 mill certificate with heat number, on request |
| Conformity document | Certificate of conformity per lot, issued in the buyer's name on request |
| Traceability | Heat number → production lot → inspection record → packing list |
| Claim window | Reported within 30 days of receipt, with photographs and the lot number |
Is the specification right? Drawing and purchase order compared line by line — dimensions, clearance, cage, seal, grease, marking. Material certificate checked against the grade. Most errors are caught here, before any metal is ground.
Is the process stable? Bore, OD and width checked against the control plan during grinding; raceway finish and clearance checked at assembly; grease fill weight checked on a sample. Trends are watched, not just individual parts.
Is this lot conforming? Sampling to ISO 2859-1, dimensional and functional checks, visual inspection, marking and packing verified. The inspection record is filed against the lot number and travels with the shipment.
| Check | Instrument | Typical tolerance | Why it matters |
|---|---|---|---|
| Bore diameter | Bore gauge / air gauge | Per ISO 492 class | Sets the shaft fit and the running clearance |
| Outside diameter | Micrometer | Per ISO 492 class | Sets the housing fit |
| Width | Micrometer / height gauge | Per ISO 492 class | Controls axial position and preload |
| Radial runout | V-block + dial gauge | µm range | Noise, vibration, spindle accuracy |
| Internal clearance | Clearance gauge | Per C-class | Heat, preload, life |
| Surface roughness | Profilometer | Ra 0.05–0.2 µm on raceways | Fatigue life and noise |
| Hardness | Rockwell tester | 58–65 HRC | Load capacity, wear |
| Noise / vibration | Anderometer / BVT | dB or µm/s by grade | The first symptom a customer notices |
| Grease fill | Weighing | ±5–10% of nominal | Lubrication life and churning |
Unless the order says otherwise, sampling follows ISO 2859-1 single sampling at AQL 1.0, normal inspection. That means the sample size and the accept/reject numbers depend on the lot size — a 50-piece lot is checked differently from a 5,000-piece lot, and the risk is stated rather than assumed.
| Lot size | Sample size | Ac | Re |
|---|---|---|---|
| 2–8 | 2 | 0 | 1 |
| 9–15 | 3 | 0 | 1 |
| 16–25 | 5 | 0 | 1 |
| 26–50 | 8 | 0 | 1 |
| 51–90 | 13 | 0 | 1 |
| 91–150 | 20 | 0 | 1 |
| 151–280 | 32 | 1 | 2 |
| 281–500 | 50 | 1 | 2 |
| 501–1,200 | 80 | 2 | 3 |
| 1,201–3,200 | 125 | 3 | 4 |
| 3,201–10,000 | 200 | 5 | 6 |
| Document | Contents | Standard or on request | Lead time impact |
|---|---|---|---|
| Certificate of conformity | Lot, quantity, specification, inspection result, date | Standard | None |
| Dimensional report | Measured values against the drawing or ISO 492 | Standard on request | None |
| EN 10204 3.1 mill certificate | Heat number, chemistry, mechanical properties | On request | Adds 2–5 days |
| First article inspection (FAI) | Full dimensional and material record for a new part | On request | Adds 3–5 days |
| RoHS / REACH declaration | Substance compliance for the part and the coating | On request | None |
| PPAP-style package | Control plan, capability, MSA, sample records | On request | Adds 1–2 weeks |
| Packing list | Carton count, weights, dimensions, marks | Standard | None |
Every lot is identified by a production lot number that links to the material heat number, the inspection record and the packing list. That chain is what makes a certificate meaningful: without it, a 3.1 certificate proves what was melted, not what is in the box. Where the order requires it, rings carry a laser-marked lot or date code so a part in service can be traced back.
We are a supplier, not a factory: our own operation is a trading and engineering desk, and the certification that matters is the producing plant's. We state which plant makes each order and provide its current certificate on request, rather than implying a certification we do not hold ourselves.
A certificate of conformity is our statement that the lot meets the purchase specification. An EN 10204 3.1 certificate is the steel mill's statement about the heat the part was made from, with chemistry and mechanical properties, signed by the mill's independent inspection representative. They answer different questions and are often needed together.
Yes, on critical dimensions and on request, at additional cost and lead time. For safety-critical parts it is usually the right call; for standard catalogue items it is not necessary and is not done by default.
Lot traceability, the producing plant's documentation, and the marking on the ring and the box. Counterfeit bearings are a real problem in this industry; we buy through authorised channels and can show the chain. The seven checks a buyer can do are in the help centre.
Send the failed part, photographs and the service history. We identify the failure mode per ISO 15243 — fatigue, wear, corrosion, electrical erosion, plastic deformation or fracture — and report whether it is a manufacturing defect or an application issue.
For automotive and medical programmes, yes: control plan, capability studies, MSA and sample records. It adds one to two weeks to the first order and is agreed at quotation stage.
Send the drawing and the standard you work to — AQL, PPAP, 3.1 certificates, 100% inspection — and we will quote the plan, the documents and the lead time.