Ordered diameter and final part size
List the supplied diameter and tolerance separately from rough-machining and finished-part dimensions. Identify the drawing revision and usable length. For stepped or locally machined stock, mark the zones controlled by each dimension so a finished bearing diameter is not mistaken for the bar purchase size.
Whether a diameter tolerance is needed
Use the tolerance class from the controlling standard and edition or state explicit upper and lower limits. Keep the units clear. Where engineering has not fixed the limits, provide the final envelope and processing requirements and request a proposed supplied size for approval before purchase.
Surface and processing route
Identify whether diameter is accepted on black, peeled, turned, ground, heat-treated, or coated material. Define any separate ovality, form, or straightness requirement instead of expecting the diameter tolerance to cover it. Check the minimum supplied size against the stock required for later clean-up.
Inspection method for the stated tolerance
Agree measurement locations and directions, excluded end zones, equipment, surface condition, and sampling. State which readings must appear on the report and how results link to the heat or lot. If independent inspection is required, include its timing and scope in the enquiry.
Diameter as upper and lower limits
Begin with the basic diameter and either an ISO 286-2 shaft tolerance class or clear upper and lower limits from the controlling product or project specification. Name the edition and keep one unit system in the contractual clause. Then state the product state: hot wrought, peeled, turned, ground, heat treated, coated, or another agreed condition. A tolerance attached to an unspecified stage cannot govern both an intermediate blank and a finished rod. Mark the controlled usable length and identify ends, chamfers, crop zones, or local features that follow different requirements.
Diameter terms to settle
| Characteristic | What it controls | Separate RFQ decision |
|---|---|---|
| Diameter limits | Permitted local size under the named size specification | Basic size, tolerance class or clear limits, state, locations, and units |
| Out-of-round or form | Variation of circular form not fully communicated by size alone | Needed form characteristic, method, section locations, and acceptance |
| Straightness or axis geometry | Departure of a line or axis over an evaluated span | ISO 1101 callout, span, datum or support basis, and end exclusions |
| Surface and coating | Material condition that can affect measurement and final size | Inspection stage, surface preparation, coating state, damage, and rework rule |
RFQ example
Item: Steel round bar to drawing [number and revision]
Material: [grade, product standard, edition, and delivery condition]
Diameter: Basic size [state] with [ISO 286-2:2010 shaft class or clear upper and lower limits]; one contractual unit system
Measured state: After [final supplier-controlled finishing, heat-treatment, or coating operation]
Controlled length: [usable length], excluding [defined end or transition zones]
Related geometry: [roundness, cylindricity, straightness, or run-out] only as separately stated drawing requirements to ISO 1101:2017
Inspection: [equipment method, locations, orientations, sampling population, out-of-limit disposition, and reinspection after rework]
Certificate: ISO 10474 document type [state type] with actual dimensional results linked to bar or lot identity
Deviations: No tolerance-system, route, or inspection-state change without written approval
Questions buyers ask
What diameter tolerance should buyers put in a steel round bar RFQ?
Buyers should use the tolerance required by the drawing, project standard, or downstream process. If it isn't fixed, state rough size, final size, surface route, application, inspection needs, and ask for review with the inquiry.
Why should rough size and final size both be included?
Rough size and final size help review machining allowance, material route, surface process, dimensional inspection, and whether the supplied bar size can support the final component requirement.
Does tolerance wording affect steel bar quotation?
Yes. Tolerance wording can affect processing route, starting size, inspection coverage, document review, packing discussion, and quotation assumptions, so it should be stated before order confirmation if specified.
RFQ checklist
- Supplied bar diameter and whether it is rough size or final size
- Final part diameter or drawing-controlled dimensions when available
- Diameter tolerance required by drawing, standard, or downstream process
- Machining allowance and expected surface route
- Delivery condition, grade standard, and equivalent grade names if allowed
- Dimensional inspection, report, and third-party inspection requirements
- Heat number or batch traceability and certificate expectation
- Length, quantity, packing, destination, and shipment document needs
- Name the basic size, tolerance class or clear limits, edition, and units.
- State the exact processing and surface state in which diameter is accepted.
- Define controlled length, measurement sections, orientations, and end exclusions.
- Add form or axis controls separately when the application needs them.
- Set sampling, out-of-limit disposition, rework, reinspection, and result traceability.
References
Inquiry support
Want us to review the RFQ before quotation?
Send the drawing or RFQ with the grade, size, condition, processing, inspection, quantity, and destination. We can flag open points before quotation.