Views: 0 Author: Site Editor Publish Time: 2026-09-03 Origin: Site
When sourcing G10 bearing steel balls for servo motor bearings, buyers need more than a nominal diameter and a grade designation. Material, ball gauge, surface condition and batch consistency must match the bearing drawing and its acceptance requirements.
A customer inquiry received by RISHENG illustrates this need: approximately 2 million G10 steel balls, with requested diameters of 6.35 mm and 15.081 mm, for servo motor bearing production. Before quoting, the purchasing specification needs to establish the exact dimensions, quantity per size and inspection criteria.
The table below provides nominal diameter conversions useful when specifying G10 bearing balls. It describes the individual ball diameter, rather than the bore, outside diameter or width of a complete bearing.
| Nominal inch diameter | exact metric diameter |
| 1/8 inch | 3.175 mm |
| 3/16 inch | 4.7625 mm |
| 1/4 inch | 6.35 mm |
| 5/16 inch | 7.9375 mm |
| 3/8 inch | 9.525 mm |
| 1/2 inch | 12.7 mm |
| 19/32 inch | 15.08125 mm |
| 5/8 inch | 15.875 mm |
| 3/4 inch | 19.05 mm |
| 1 inch | 25.4 mm |
6.35 mm G10 steel balls and 1/4-inch G10 bearing balls share the same nominal diameter. A purchase specification must also state the material, ball gauge or agreed size deviation, and inspection standard.
Two suppliers quoting “6.35 mm G10” may still be quoting different size groups or additional quality requirements. Compare the complete specification before comparing prices.
If a drawing specifies 19/32 inch, the exact metric equivalent is 15.08125 mm. Writing 15.081 mm instead changes the stated reference by 0.00025 mm, or 0.25 μm.
Confirm whether 15.081 mm is the intended metric nominal diameter or a rounded description of an inch size. This difference concerns the nominal reference; it should not be confused with the single-ball diameter variation allowed by a precision grade.
A 16 mm steel ball is a separate size, differing from 15.081 mm by 0.919 mm. It cannot be treated as a substitute without approval of the bearing design.
G10 is a precision grade covering geometric and surface characteristics. It does not identify the steel material or guarantee a finished bearing’s noise performance.
The following G10 reference limits are published in TN UK’s ISO 3290-1 comparison table:
| Characteristic | G10 reference maximum |
| Single-ball diameter variation | 0.25 μm |
| Deviation from spherical form | 0.25 μm |
| Ball lot diameter variation | 0.50 μm |
| Surface roughness, Ra | 0.020 μm |
G10 does not mean a universal nominal-diameter tolerance of ±0.25 μm. The variation measured on one ball, the variation within a lot and the position of the supplied size group are different requirements.
Specify the required ball gauge, plus subgauge where applicable, or an agreed mean-diameter deviation. This makes the requested size group clear to the bearing steel ball supplier.
RISHENG manufactures AISI 52100 / GCr15 bearing steel balls. Its published product range includes G10–G1000 precision grades and a hardness range of HRC 60–66.
For a servo motor bearing project, the required material and hardness must come from the approved specification. The inquiry described above establishes a G10 requirement but does not yet confirm the material.
When requesting G10 chrome steel balls, identify the material standard, heat-treatment condition and required inspection documents. Related designations such as AISI 52100, GCr15, 100Cr6 and SUJ2 should be checked against the applicable standards before approving a substitution.
A catalog hardness range is a starting point for discussion. If the bearing drawing requires a narrower range, include it in the quotation request.
A ball may meet its specified geometric grade while the assembled bearing still requires further noise and vibration evaluation.
Three questions help make the quality requirement measurable:
What surface limits apply? Agree on waviness limits, defect criteria and the measurement method where required.
What cleanliness condition is needed? Define acceptable residues and the cleaning or preservation condition expected before assembly.
How will performance be accepted? State the assembled-bearing test method, operating speed, load and noise or vibration limits.
G10 should therefore appear alongside these requirements, rather than replace them. Sample approval should cover the characteristics relevant to the actual bearing application.
Precision ball production typically includes forming, flash removal, heat treatment, grinding, lapping and cleaning. Heat treatment establishes the required material condition; subsequent finishing brings the ball toward its final geometry and surface requirements.
For buyers, the useful question is how the finished lot will be verified. Ask the precision bearing ball manufacturer to identify:
The method used to measure diameter and classify ball size groups;
The equipment used for spherical-form and surface-roughness inspection;
The sampling plan or screening scope for each characteristic;
The records connecting finished balls to material and production batches.
A polished appearance alone cannot demonstrate G10 compliance. The inspection report should identify the measured characteristics, acceptance limits and lot reference.
For more detail on finishing, read RISHENG’s steel ball lapping process guide.
Suitability depends on the bearing design and its operating requirements. Use the precision grade specified by the bearing manufacturer, together with the required material, size group and performance checks.
For purchasing, use the complete bearing designation and an approved ball drawing or manufacturer-confirmed ball specification. Do not treat the basic bearing number as a complete steel ball order specification.
Do not assume so. First establish whether the nominal dimension is metric or derived from 19/32 inch, then confirm the permitted deviation and size group.
No. G10 addresses specified ball characteristics. A noise limit or service-life claim requires separate evidence relevant to the assembled bearing and operating conditions.
Request a quotation against the drawing, material standard, precision standard, exact diameter, ball gauge, hardness and quantity per size. Specify which inspection results and traceability documents must accompany delivery.
Include the proposed delivery schedule in the inquiry. Confirm quantities, lot identification and acceptance requirements for each shipment before agreeing on the supply plan.
