Reading a Bearing Inspection Report: What Each Number Means

A real inspection report has 7 sections — dimensional check, radial play, rotation, vibration, visual, material certificate, and batch traceability. Here is what to look at, what red lines to hold, and what to ask for when a number falls outside your spec.

When a supplier offers to send 'an inspection report,' most first-time importers nod, file it, and never read it. That is a missed quality lever. A real factory inspection report has seven sections, and each one is something you can hold the supplier to. Here is how to read it.

Section 1 — Dimensional inspection:

Three measurements per bearing sample: bore (inner diameter), outer diameter, and width. Each has a target value and a tolerance band defined by ISO 492. The most common tolerance grades in motorcycle and pump bearings are P0 (normal), P6 (one grade better), and P5 (precision).

For a 6301-2RS at P0: bore 12 +0/−0.008mm, OD 37 +0/−0.011mm, width 12 +0/−0.120mm. If the report shows bore at 11.985mm, that is outside the P0 tolerance — reject or renegotiate.

Section 2 — Radial play (radial internal clearance):

Listed in μm. Should match the clearance class in the part number (CN, C3, C4). Cross-reference against ISO 5753. If the part number says '6205-2RS C3' (range 13–28 μm) but the report shows 9 μm, the bearing is actually CN — not what you ordered.

Section 3 — Rotation smoothness:

Usually reported as a pass/fail or graded A/B/C. The factory operator rotates the bearing by hand under light axial load and listens for any roughness, grittiness, or detent. For high-speed wheel applications, anything less than A is a problem.

Better factories report rotation in terms of running torque (mN·m or N·mm) — measurable, repeatable, not subjective.

Section 4 — Vibration (V-level):

Vibration is measured on a calibrated test stand at a specified RPM. The result is grouped into a 'V-level': V1 is standard, V2 is low-vibration (quieter, better for motors), V3 is ultra-low (precision applications). For motorcycle wheels V1 is acceptable; for pump and motor bearings, ask for V2 minimum.

Section 5 — Visual inspection:

A trained inspector checks for surface defects: rust spots, dents on the raceway, seal deformation, cage damage, ink or grease smearing on the outside. A good report names the defect rate (e.g. '0 defects in 50 sampled' or '2 defects in 50, both seal lip cosmetic'). Reject lots with raceway defects regardless of count.

Section 6 — Material certificate:

States the steel grade for the rings and rolling elements. The industry standard is GCr15 (Chinese GB/T standard, equivalent to AISI 52100 / SAE 52100). Cheap bearings substitute carbon steel or low-chromium steel — visually identical but with 30–40% lower fatigue life under load. Insist on GCr15 in writing and ask for a mill test certificate (MTC) on a sample lot every 6 months.

Section 7 — Lot and batch traceability:

Every carton should be marked with a batch code that ties back to a specific production date, raw material lot, and inspection report. This matters when a failure happens in the field: you can ask for analysis of the same batch instead of vague 'random sample' replacement.

What to do when a number fails your spec:

1. Document the failure with photos of the report and the carton batch code.

2. Request the same SKU from a different batch and re-test.

3. If the failure repeats: hold the next shipment payment, request third-party inspection (SGS, BV, Intertek) at the factory before container loading — cost is $200–400 per inspection, and the supplier usually pays if quality is the issue.

Frequency of inspection reports to request:

On every shipment: a sampled inspection report (typically 5 pcs per SKU). On every quarterly material change: a fresh MTC. On every new supplier or new manufacturing batch: a full first-article report.

Need a sample FULI inspection report? Request one with your trial order. WhatsApp +86 152 6352 1305 and ask for the inspection report template — a real, anonymized example so you know exactly what to expect.