Bright Bar Size & Tolerance Tables

"h9" is an ISO 286-2 tolerance class applied to shaft-type features. The "h" means the upper deviation is always zero — the bar can never exceed the nominal size. The "9" is the IT (International Tolerance) grade number, which sets how large the tolerance band is. So h9 on a 20mm bar means the bar must be between 19.948mm and 20.000mm. It is commonly specified on precision shafts running in bearings or close-clearance bores.

Standard cold-drawn round bright bar is manufactured to h10 tolerance per BS EN 10278. However, the actual diameter will typically be within the h10 band — many bars from quality mills routinely sit within the tighter h9 band even without the formal ground-bar specification. If your application requires guaranteed h9, specify precision ground bar and confirm with your supplier that the grade and condition are appropriate.

Yes. Standard ground bright bar is supplied to h9, but precision centreless ground bar can be produced to the tighter ISO 286-2 classes h8, h7 and h6 on request. For example, a 20mm bar to h6 has a tolerance of just +0 / −0.013mm (19.987–20.000mm), against −0.052mm for h9. h6 and h7 are available up to 120mm diameter; h8 up to 250mm. These tighter classes suit bearing journals, close-clearance shafts and precision hydraulic components — specify the class at time of enquiry.

BS EN 10278 specifies that tolerances for low-carbon and free-cutting steels (carbon ≤ 0.20%) are the base values in the standard. For all other grades — including the medium-carbon and alloy steels such as EN8 (080M40), EN19 (708M40) and EN24T (817M40T) — the tolerances are increased by 50%. This is because higher-carbon and alloy grades are harder to cold-draw to tighter dimensions. A 30mm EN1A bar to h10 has a tolerance of −0.084mm; a 30mm EN24T bar to h10 has a tolerance of −0.126mm.

Per BS EN 10278, dimensional measurements must be taken at least 150mm from either end of the bar. The ends are excluded because they are subject to slightly different deformation during drawing and may not be representative of the bar body. Straightness is also assessed using a 1 metre straight edge placed at least 150mm from each end.

Yes. Parkside Steel can supply bright bar with a BS EN 10204:2004 Type 3.1 material test certificate on request. The 3.1 certificate is issued by the mill and includes the heat number, chemical composition and mechanical test results. Please specify this requirement at time of enquiry — it should be noted on your purchase order. Some grades and sizes may require advance ordering to secure certified stock.

Both h9 and JS9 (sometimes written j9 or ±IT9/2) use the same total tolerance band width — IT grade 9. The difference is the position of the band relative to the nominal size. h9 is all-minus: the upper limit is zero and the bar can only be equal to or under nominal size. JS9 (or j9) splits the tolerance equally either side of nominal — so a 20mm JS9 bar would be 20mm ±0.026mm. JS9 is less commonly specified for bright bar but may appear on older drawings or where a bore and shaft pair requires a different fit condition.