Which bearings do small motors use?

Deep-groove ball bearings with seals or shields, typically 608, 6000, 6001 or 6201 series with C3 clearance, low-noise grade and long-life grease. Miniature motors may use 69x or 68x series.

Press-fitting the inner ring on the shaft and running warm both reduce internal clearance. C3 leaves enough clearance after mounting to avoid preload, heat and noise.

How do I avoid counterfeit bearings?

Buy branded bearings only through the brand's authorised distributors, check packaging and markings, and ask for a brand verification for large orders. For domestic brands, audit the factory and run noise and vibration tests on samples.

Purchased component

Deep-groove Ball Bearing

Ring forging & turning → Heat treatment → Grinding → Superfinishing → Cleaning, assembly, greasing & sealing → Vibration & noise test

✓ Expert reviewed All content on this page has been reviewed by a senior motor engineer.

Process flow

6 main process steps, with the equipment and instruments used at each step, their main suppliers, and the technical control points.

1
Ring forging & turning
GCr15 (52100) bearing steel is forged or turned into ring blanks.
⚙ CNC Lathe / Turning CentreAutomated
International
MazakGuangzhou, OkumaGuangzhou, DMG MORI
Mainland China
MinjiaGuangzhou, JSWAYZhongshan, Haitian Precision
Technical control points:
- ▪Steel cleanliness and structure — Oxygen ≤ 9 ppm, Ti ≤ 30 ppm; carbide network within grade (GB/T 18254)Check: Mill certificate and metallography; every heat
- ▪Blank dimensions — Per drawing with heat-treatment and grinding allowanceCheck: Gauges; first piece and SPC
2
Heat treatment
Through-hardening and tempering to about HRC 60–64.
⚙ Heat-treatment Furnace / Induction HardenerAutomated
International
Ipsen, Aichelin
Mainland China
To be added
⚙ Hardness TesterTest instrumentSemi-automaticManual
International
To be added
Mainland China
To be added
Technical control points:
- ▪Hardness — HRC 60–64; variation within a ring ≤ 1 HRCCheck: Rockwell tester; every batch
- ▪Retained austenite — Low (e.g. ≤ 8–10%) or stabilised for dimensional stabilityCheck: XRD; process qualification and periodic
- ▪Microstructure and distortion — Fine martensite, no troostite; distortion within grinding allowanceCheck: Metallography and dimensional check; every batch
3
Grinding
Faces, outer diameter, bore and raceways are ground.
⚙ Bearing Ring GrindersAutomated
International
To be added
Mainland China
To be added
⚙ CMM, Roundness & Runout GaugesTest instrumentSemi-automaticManual
International
MitutoyoDongguan, HexagonGuangzhou, MarpossShenzhen+1 more →
Mainland China
To be added
Technical control points:
- ▪Raceway curvature and position — Groove radius ≈ 0.515–0.53 × ball diameter; position per designCheck: Contour gauge; sampling
- ▪Roundness and waviness — Raceway roundness ≤ 1–2 µm; waviness per noise gradeCheck: Roundness tester; sampling
- ▪Grinding burn — NoneCheck: Nital etch or Barkhausen noise; sampling
4
Superfinishing
Raceways are superfinished for low roughness and low noise.
⚙ Superfinishing MachineAutomated
International
Thielenhaus, Supfina
Mainland China
To be added
Technical control points:
- ▪Raceway roughness — Ra ≈ 0.02–0.05 µmCheck: Profilometer; sampling
- ▪Waviness — Within limit for the target vibration gradeCheck: Waviness analyser; sampling
5
Cleaning, assembly, greasing & sealing
Rings and balls are cleaned, matched for clearance, assembled with the cage, greased and shielded.
⚙ Bearing Assembly, Greasing & Sealing LineAutomated
International
To be added
Mainland China
To be added
Technical control points:
- ▪Radial internal clearance — Per class, e.g. 6000 C3: 11–25 µm (ISO 5753-1)Check: Clearance gauge; 100%
- ▪Grease type and quantity — Specified low-noise grease, fill ≈ 25–35% of free volumeCheck: Automatic dispenser; weighing sampling
- ▪Cleanliness — Particle count within specCheck: Particle analysis; sampling
6
Vibration & noise test
Every bearing is spun and its vibration measured to classify the grade.
⚙ Bearing Vibration / Noise TesterTest instrumentAutomatedSemi-automatic
International
To be added
Mainland China
To be added
Technical control points:
- ▪Vibration grade — Z2 / V2 standard; Z3 / V3 for low-noise motors (GB/T 24610)Check: Vibration tester; 100%
- ▪Abnormal noise — None (no click, crackle or periodic noise)Check: Acoustic / operator listening; 100%
- ▪Rotation — Smooth, no bindingCheck: Hand / machine spin; 100%

Incoming inspection & approval tests

Vibration grade (Z1 / Z2 / Z3 or V)GB/T 24610, ISO 15242
Noise and abnormal soundIncoming sampling
Radial internal clearanceAgreed value, e.g. C3
High/low-temperature running and accelerated lifeDuring supplier approval
Grease low-temperature starting torqueLow-temperature applications

Buyer FAQ

Which bearings do small motors use?: Deep-groove ball bearings with seals or shields, typically 608, 6000, 6001 or 6201 series with C3 clearance, low-noise grade and long-life grease. Miniature motors may use 69x or 68x series.
Why C3 clearance?: Press-fitting the inner ring on the shaft and running warm both reduce internal clearance. C3 leaves enough clearance after mounting to avoid preload, heat and noise.
How do I avoid counterfeit bearings?: Buy branded bearings only through the brand's authorised distributors, check packaging and markings, and ask for a brand verification for large orders. For domestic brands, audit the factory and run noise and vibration tests on samples.

Supply chain / regions

Bearing factories are mostly outside the Pearl River Delta (Zhejiang, Liaoning, Henan, Japan); the Pearl River Delta has brand sales offices in Guangzhou and Shenzhen and local makers of miniature bearings in Dongguan and Shenzhen. Buy branded bearings only through authorised channels to avoid counterfeits.

Representative suppliers

Used in

57 mm Inner-rotor BLDC MotorBearings · Specification: 608ZZ / 6000ZZ / 6001ZZ, C3 clearance, low-noise grease
42 mm Two-phase Hybrid Stepper Motor (NEMA 17)Bearings · Specification: 625ZZ or 625-2RS, low-noise grade (Z2 / V2 or better)
57 mm Two-phase Hybrid Stepper Motor (NEMA 23)Bearings · Specification: Deep-groove ball bearings sized to the shaft (e.g. 608ZZ / 608-2RS), low-noise grade (Z2 / V2 or better)
37 mm Brushed DC Gear Motor (spur gearbox)Output bearings · Specification: Small deep-groove ball bearings (sintered bushings on low-cost versions)
86 mm Two-phase Hybrid Stepper Motor (NEMA 34)Bearings · Specification: Deep-groove ball bearings sized to the shaft (e.g. 6201 / 6202 series, ZZ or 2RS), low-noise grade
57 mm Integrated BLDC Motor (built-in driver)Bearings · Specification: 608ZZ / 6000ZZ / 6001ZZ, C3 clearance, low-noise grease
70 mm Outer-rotor BLDC MotorBearings · Specification: 608ZZ / 6000ZZ, C3 clearance, low-noise grease
AC Servo Motor (60–130 mm flange)Bearings · Specification: 6002 / 6203 / 6204 class, 2RS or ZZ, C3, high-speed low-noise grease
Coreless Brushed DC Motor (16–22 mm)Bearings · Specification: Miniature deep-groove ball bearings (e.g. 3 × 7 × 3 mm), low-noise grade, high-speed grease
IEC Three-phase Induction Motor (frames 80–160, IE3)Bearings · Specification: Deep-groove 6204 to 6309, 2Z / 2RS, C3 clearance, grease rated 120 °C or higher
Direct-drive Torque Motor & Robot Joint ModuleCrossed-roller bearing · Specification: Thin-section crossed-roller bearing, P5 or better, preloaded (C1 / zero clearance)