Stainless Steel Bar Tolerance Chart (h9, h10, h11): ISO 286-2 Guide

Introduction

A drawing that says 20 mm h9 is not asking for an approximate 20 mm stainless steel bar. It sets a permitted size window from 20.000 to 19.948 mm under the ISO 286-2 shaft tolerance table. That difference affects incoming inspection, machining allowance and whether the bar feeds consistently through a collet or guide bush.

This guide gives buyers a practical h9 vs h10 vs h11 stainless steel bar tolerance chart. It also explains what the tolerance code does not cover, which production routes may hold the requested size and what evidence to request before shipment.

Quick Answer

For stainless steel bar ordered to a shaft or external-size tolerance, h9 is tighter than h10, and h10 is tighter than h11. The lowercase h places the upper deviation at zero, so the actual size may equal the nominal size but must not exceed it. The lower limit depends on the nominal-size range and tolerance grade.

Before ordering, confirm six points:

• Which dimension carries the tolerance: round-bar diameter, hex-bar across-flats size or square-bar side size.
• Whether the drawing calls for h9, h10, h11 or a separate plus/minus limit.
• Which process route will hold it: cold drawn, turned or peeled, or centerless ground.
• Whether straightness, roundness and surface roughness need separate limits.
• What dimensional inspection record will be supplied.
• Whether the MTC, heat number, labels and packing list match the same batch.

Use the stainless steel bar tolerance lookup for a quick nominal-size check. The drawing and purchase order still control final acceptance.

h9 vs h10 vs h11 tolerance chart

These examples show the permitted size range for three common nominal round-bar diameters. Values follow the size intervals used in ISO 286-2.

The table is a sourcing aid, not a replacement for the complete standard. Check the edition and tolerance wording named by the drawing or project documents.

ISO 286-2 lower deviations for h9, h10 and h11

For an h shaft tolerance, the upper deviation is zero. The table below combines the lower deviations used for nominal sizes up to 120 mm. All values are in millimeters.

A boundary value belongs to the interval stated by the standard. For example, 10 mm uses the over-6-to-10-mm row, while a size above 10 mm moves to the next interval.

What the lowercase h means on a bar drawing

The letter and number do different jobs. Lowercase h identifies the tolerance-zone position for an external feature such as a shaft. Its upper deviation is zero. The number identifies the tolerance grade, with a lower number giving a narrower zone.

That wording matters in purchasing. A quote for 20 mm bright round bar does not automatically mean 20 mm h9. The supplier needs the tolerance class or explicit limits before selecting stock, production and inspection routes.

The dimension must also be clear. Round bar is normally controlled by diameter. A stainless steel hex bar inquiry normally uses across-flats size, while stainless steel square bar uses side size. Do not transfer a round-bar h9 note to another shape without identifying the dimension it applies to.

Cold drawn, peeled and ground bar do not mean the same thing

A finish name is not proof of a tolerance class. The achievable range depends on diameter, grade, starting stock, straightening, finishing equipment, length and the mill's agreed inspection method.

The cold drawn stainless steel bar page explains the cold-finishing route. For tighter cylindrical work, compare the centerless ground stainless steel bar page before fixing the RFQ wording.

When h9 is justified, and when h10 or h11 is enough

The tightest available class is not automatically the best purchase. Start with the finished part and the first machining operation.

For general round-bar sourcing, see the stainless steel round bar supply page. It separates diameter tolerance from straightness, roundness, surface condition and cut length.

What h9 does not control

An h9 callout controls a size limit. By itself, it does not define every characteristic that matters to CNC production. Add separate requirements when the application needs them:

• Straightness: important for long bars, bar feeders and rotating shafts.
• Roundness or ovality: important where the bar rotates or fits a close cylindrical feature.
• Surface roughness: important for finished shafts, seals and visible components.
• Decarburization or surface-defect limits: relevant only when the grade, process or application calls for them.
• Cut-length tolerance and end condition: important for automatic loading, fixed blanks and packing.

This is a common source of disputes. A batch can pass the h9 diameter limits and still be unsuitable if the drawing also needed tighter straightness or surface roughness but the purchase order never stated it.

What to inspect before shipment

A Mill Test Certificate does not prove h9 tolerance. The MTC identifies the material batch through grade, chemistry, mechanical properties, heat number and standard wording. Dimensional acceptance needs a separate inspection record or agreed measurement evidence.

Before releasing a precision bar shipment, ask for:

• the ordered nominal size and tolerance class on the inspection record;
• measured values taken from the agreed number of bars and positions;
• the measurement method and instrument type when the project requires them;
• straightness, roundness or roughness results when those limits are on the PO;
• bar or bundle labels showing the same heat number as the MTC and packing list;
• photos of the bundle condition, end protection and shipping marks.

For document traceability, use the stainless steel MTC checklist before shipment release. Keep the MTC check and the dimensional check as two connected but separate approval steps.

RFQ wording example

The cleanest RFQ states the controlled dimension and the evidence required. A Thailand machining buyer could write:

SUS304 cold-drawn round bar, diameter 20 mm h9, straightness max. 1 mm/m, 3 m fixed length, 500 kg trial order. MTC and dimensional inspection record required. Please confirm surface route, cut-length tolerance, packing and FOB price. Destination: Laem Chabang, Thailand.

Do not copy the straightness value into another order unless it comes from the drawing or production requirement. It is included here only to show that straightness must be written separately from h9.

For hex bar, replace diameter with across-flats size. For square bar, state the side size. If the drawing mixes metric and imperial dimensions, identify which unit controls final acceptance; a nominal conversion error can be larger than the entire h9 tolerance zone.

Common purchasing mistakes

• Ordering bright bar and assuming the word bright guarantees h9.
• Requesting h9 without naming the dimension or product shape.
• Checking the MTC but not asking for measured dimensions.
• Adding h9 while leaving straightness, roughness and cut length undefined.
• Converting a metric drawing to the nearest inch stock size without converting the limits.
• Paying for h9 when the first production step removes enough material to make h10 or h11 sufficient.

Sources and scope

The tolerance values in this guide are based on ISO 286-2:2010, Geometrical product specifications (GPS) - ISO code system for tolerances on linear sizes - Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts. ISO 286-1:2010 provides the basis of the code system.

Always follow the standard edition, drawing and customer-specific acceptance criteria named by the order. The tables above cover selected h9, h10 and h11 external-size limits up to 120 mm; they are not a complete reproduction of ISO 286-2.

Conclusion

The useful question is not whether h9 is better than h10 or h11. It is whether the bar's starting-size window matches the machining route and final part. h9 can make sense for controlled feeding and shaft work. h10 often suits general machining stock. h11 may be sufficient when heavier machining or later grinding follows.

Write the controlled dimension, process route and separate form or surface limits into the RFQ. Then match the dimensional report to the bar labels, MTC and packing list before shipment release.

Frequently Asked Questions (FAQ)

CTA

Send the grade, bar shape, nominal size, tolerance class, surface route, straightness if critical, length, quantity, inspection record, MTC requirement and destination through the contact page. FX Stainless Steel will check the available production route, packing plan and quotation basis for your order.