Tolerance Class (h8, h9, h10, h11)
The ISO limits that fix how far under nominal a bright bar diameter may sit — h8 being the tightest and h11 the loosest, with the permitted band widening as diameter increases.
What the class actually means
All h classes are unilateral minus: the bar is never oversize, only undersize by a permitted amount. On a 20 mm bar, h8 allows 0 to -0.033 mm, h9 allows 0 to -0.052 mm, h10 allows 0 to -0.084 mm and h11 allows 0 to -0.130 mm. At 50 mm the same classes open to -0.039, -0.062, -0.100 and -0.160 mm.
Matching class to finish
Cold drawing holds h9 to h11. Smooth turning holds h10 to h11. Centreless grinding is the only route to h8 reliably, and it is what you specify when a bearing, seal or bush seats directly on the bar without a finishing cut. Asking for h8 on cold drawn bar costs money and will not be met.
Related terms
Where this applies
Free Cutting Bright Bars, Stainless Bright Bars
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