ISO 286 · 1/4″ nominal (6.35 mm)

1/4″ shaft tolerances, every fit class

Every ISO 286 shaft class at a 1/4″ nominal, computed for exactly this diameter: the limits the configurator stamps when you pick a class on a 1/4″ seat, the IT grade widths behind them, and the tolerance the bar itself arrives in.

At a 1/4″ nominal (6.35 mm) ISO 286 places the diameter in its over 6 to 10 mm size step, so every class on this page takes its width from one row of the IT table: IT5 is 0.0002″, IT6 0.0004″, IT7 0.0006″ wide here. The letter then decides where that band sits against 0.2500″.

The tightest class on the page is k5 at 0.0002″; the widest is d9 at 0.0014″. The lowest limit on the page is 0.2470″ (d9 minimum) and the highest 0.2513″ (s6 maximum): a 0.0043″ spread between the loosest clearance and the heaviest press fit at this one diameter.

Pick any of these classes on a 1/4″ diameter in the configurator and the drawing carries exactly these limits; the engine computes them from the standard for the diameter you enter, so a nominal between the sizes in this series resolves the same way.

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Every fit class at 1/4″

Deviations from the 0.2500″ nominal in inches at 0.0001 in resolution; max and min are the finished diameter limits. Each class links to its own page with this class at every nominal.

Download this table (CSV)

IT grade widths at 1/4″

Band width (upper minus lower) of the h class at each grade. The letter of a class only moves the band; the grade alone sets how wide it is, so these widths apply to every class on this page.

As-supplied bar tolerance at 1/4″

Mill tolerance of the round bar as it arrives from the mill, for the grades the configurator offers. A fit class is cut to the limits above regardless; only a diameter left as supplied under a mill-finish OD carries the bar tolerance.

Part of Shaft fits and tolerances. Other pages in the series: d9 · e8 · f7 · g6 · h6 · h7 · h8 · js6 · j6 · k5 · k6 · m6 · n6 · p6 · r6 · s6 · 3/8″ · 1/2″ · 5/8″ · 3/4″ · 7/8″ · 1″ · 1-1/8″ · 1-1/4″ · 1-3/8″ · 1-1/2″ · 1-3/4″ · 2″ · 2-1/2″ · 3″ · 4″ · 20 mm · 25 mm · 30 mm · 35 mm · 40 mm · 45 mm · 50 mm · 55 mm · 60 mm · 65 mm.

Clearance, transition and interference at 1/4″

Against a nominal 0.2500″ (H-basis) bore the clearance classes always leave a gap: f7 at least 0.0005″, g6 at least 0.0002″, while h6 and h7 touch nominal on the high side and leave a gap only as the shaft runs toward its minimum (0.2496″ for h6, 0.2494″ for h7).

The transition classes cross nominal: js6 is ±0.0002″, k5 runs +.0000 to +.0003, k6 +.0000 to +.0004; snug in a nominal bore, still off with an arbor press.

The interference classes are oversize throughout: p6 by 0.0006″ to 0.0009″, s6 by 0.0009″ to 0.0013″, before the bore's own tolerance is added. Size press force and hub stress from the maximum.

Fit class versus bar tolerance

The bar a 1/4″ shaft is turned from has its own mill tolerance, listed in the third table. Cold-finished low-carbon steel bar (1018, 12L14) arrives at +.0000/-.0020 at this size, a 0.0020″ band, which is 5.6 times the IT6 width of 0.0004″.

A fit class is cut, so the bar's band never reaches the finished diameter. It matters for one case: a round diameter equal to the bar size and left as supplied under a mill-finish OD. That surface keeps the mill's tolerance and finish, and the drawing calls it out as the bar tolerance rather than a fit class.

Catalog parts with a 1/4″ diameter

Parts in the catalog that carry a 1/4″ diameter on at least one segment: 1-1/2″ Bore Light-Duty / Pneumatic Cylinder Tie Rod, 1/4″ × 1-1/16″ Idler Shaft, 3/8″ × 1-7/32″ Idler Shaft, 1/2″ × 12″ Mixer Shaft, 1/2″ × 48″ Mixer Shaft. Open one and the fit class on that diameter is already set; change it and the limits follow this table.

Related: All fit classes · Surface finish reference · Pump shafts · Motor shafts.

Frequently Asked Questions

These references are for specifying a part; every value here is one the configurator applies when you build one. Numbers are representative of the standard; check them against your part and its mating components before ordering. See all guides on the guides page.