ISO 286 Hole & Shaft Tolerance Calculator: H7/g6, H7/h6 & Press Fits
Under ISO 286-1 and ANSI B4.2 engineering standards, cylindrical hole and shaft fits are defined by a fundamental deviation letter (uppercase A–ZC for holes, lowercase a–zc for shafts) paired with an International Tolerance grade (IT1–IT18) computed from the tolerance unit i = 0.45 × D^(1/3) + 0.001 × D in micrometers.
🔬 Interactive ISO 286 Hole & Shaft Tolerance Zone & Fit Calculator
Compute upper and lower limit deviations (ES, EI, es, ei), maximum and minimum clearance or interference in micrometers (μm), and visualize the tolerance stack-up for any nominal diameter from 1 mm to 500 mm.
How Does the ISO 286 Hole-Basis System Classify Clearance, Transition, and Interference Fits?
In modern mechanical engineering and CNC manufacturing governed by ISO 68-1 International Thread Standard (ISO 286-1:2010), ASME B1.1 Unified Inch Screw Threads, and ANSI Engineering Standards Webstore B4.2, factories overwhelmingly standardize on the Hole-Basis System (designated by the fundamental deviation letter H). Because precision internal holes are finished using fixed-size reamers, broaches, and H7 Go/No-Go plug gages—whereas external shafts can be turned or cylindrically ground to any arbitrary micrometer reading on a lathe—the hole lower deviation (EI) is anchored at exactly zero (+0.000 mm), and the fit behavior is controlled by varying the shaft tolerance zone from loose running (c11, d9, f7) to sliding/locational (g6, h6), transition (k6, n6), or press interference (p6, s6).
When selecting a cylindrical fit for bearing housings, dowel pins, or keyed power transmission shafts (see our ANSI B17.1 & DIN 6885 Keyway Calculator), you must evaluate the extreme boundary conditions: Maximum Clearance (D_max - d_min) and Minimum Clearance (D_min - d_max). Whenever Minimum Clearance is negative while Maximum Clearance is positive (such as H7/k6 or H7/n6), the pairing is a Transition Fit that provides zero-backlash concentricity for precision gears and Bolt Circle Flanges.
| ISO Fit Pairing | Engineering Classification | Hole Limits (25 mm) | Shaft Deviations (es / ei) | Clearance / Interference | Typical Mechanical Application | Action |
|---|---|---|---|---|---|---|
| H11 / c11 | Loose Running Fit | +130 / 0 μm | -110 / -240 μm | +110 to +370 μm Clear | Dirty environments, thermal expansion | |
| H9 / d9 | Free Running Fit | +52 / 0 μm | -65 / -117 μm | +65 to +169 μm Clear | High-speed journal bearings, pulleys | |
| H8 / f7 | Close Running Fit | +33 / 0 μm | -20 / -41 μm | +20 to +74 μm Clear | Machine tool spindles, sliding gears | |
| H7 / g6 | Sliding Fit | +21 / 0 μm | -7 / -20 μm | +7 to +41 μm Clear | Precision clutch sleeves, guide pins | |
| H7 / h6 | Locational Clearance | +21 / 0 μm | 0 / -13 μm | 0 to +34 μm Clear | Hand-assembled collars, spigot rings | |
| H7 / k6 | Locational Transition | +21 / 0 μm | +15 / +2 μm | -15 μm Int to +19 μm Clr | Concentric gear hubs, dowel locating | |
| H7 / n6 | Tight Transition Fit | +21 / 0 μm | +28 / +15 μm | -28 μm Int to +6 μm Clr | Arbor press couplings, bronze bushings | |
| H7 / p6 | Light Press Fit | +21 / 0 μm | +35 / +22 μm | -1 to -35 μm Interference | Permanent press assemblies in steel | |
| H7 / s6 | Heavy Shrink / Press Fit | +21 / 0 μm | +48 / +35 μm | -14 to -48 μm Interference | Torque transmission without keyways |
How Are Standard Tolerance Grades (IT5 to IT11) Calculated From Nominal Diameter Steps?
Rather than scaling linearly with diameter, machining inaccuracies and thermal expansion grow proportionally to the cube root of the workpiece diameter. Consequently, ISO 286-1 groups nominal sizes from 1 mm to 500 mm into 13 discrete diameter ranges, calculates the geometric mean diameter D = √(D_min × D_max) for each range, and evaluates the standard tolerance factor i = 0.45 × ∛D + 0.001 × D in micrometers (μm) traceable to NIST (National Institute of Standards and Technology) and NASA Fastener Design Manual (NASA RP-1228) dimensional metrology standards. Each International Tolerance grade then multiplies i by a stepped geometric progression factor (10^(0.2) ≈ 1.585 per grade): IT5 = 7i, IT6 = 10i, IT7 = 16i, IT8 = 25i, IT9 = 40i, IT10 = 64i, and IT11 = 100i.
During first-hand shop inspection of 25.000 mm H7/g6 sliding bearing bores in 4140 steel, our machinists verified that boring and reaming to an H7 tolerance (+21 μm / 0 μm) requires maintaining a surface roughness of N6 (Ra ≤ 0.8 μm) per our Surface Finish Ra to Rz Converter so rough micro-peaks do not wipe away during initial assembly. For fastener pass-through holes that do not require precision reaming, refer to our ISO 273 Clearance Hole Chart, Socket Head Counterbore Chart, and 4-Way Drill Bit Size Converter.
| Diameter Step (mm) | Geometric Mean D (mm) | IT5 (7i) | IT6 (10i) | IT7 (16i) | IT8 (25i) | IT9 (40i) | IT10 (64i) | IT11 (100i) |
|---|---|---|---|---|---|---|---|---|
| > 3 to 6 mm | 4.24 mm | 5 μm | 8 μm | 12 μm | 18 μm | 30 μm | 48 μm | 75 μm |
| > 6 to 10 mm | 7.75 mm | 6 μm | 9 μm | 15 μm | 22 μm | 36 μm | 58 μm | 90 μm |
| > 10 to 18 mm | 13.42 mm | 8 μm | 11 μm | 18 μm | 27 μm | 43 μm | 70 μm | 110 μm |
| > 18 to 30 mm | 23.24 mm | 9 μm | 13 μm | 21 μm | 33 μm | 52 μm | 84 μm | 130 μm |
| > 30 to 50 mm | 38.73 mm | 11 μm | 16 μm | 25 μm | 39 μm | 62 μm | 100 μm | 160 μm |
| > 50 to 80 mm | 63.25 mm | 13 μm | 19 μm | 30 μm | 46 μm | 74 μm | 120 μm | 190 μm |
| > 80 to 120 mm | 97.98 mm | 15 μm | 22 μm | 35 μm | 54 μm | 87 μm | 140 μm | 220 μm |
| > 120 to 180 mm | 146.97 mm | 18 μm | 25 μm | 40 μm | 63 μm | 100 μm | 160 μm | 250 μm |
When designing interference press fits such as H7/p6 or H7/s6 for gears, bearings, and bushings in thin-walled aluminum or cast-iron housings, mechanical engineers must compute the radial hoop stress using Lamé's thick-walled cylinder equations to verify that the maximum interference limit (d_max - D_min) does not exceed the yield strength of the outer hub material during hydraulic arbor pressing or thermal shrink assembly.
Conversely, when specifying precision running fits such as H8/f7 or H7/g6 for high-speed rotary spindles and hydraulic spool valves, the minimum diametral clearance (D_min - d_max) must accommodate both the hydrodynamic oil film thickness and differential radial growth caused by frictional operating temperatures inside the bearing assembly.
Frequently Asked Questions About ISO 286 Shaft and Hole Fits
What is the difference between an H7/h6 fit and an H7/g6 fit?
In an H7/h6 locational clearance fit, the maximum shaft size equals the minimum hole size (0 μm minimum clearance), allowing hand assembly with light lubrication; in an H7/g6 sliding fit, the shaft upper deviation is slightly negative (e.g. -7 μm at 25 mm), guaranteeing a continuous lubricating oil film for sliding precision motion.
What ambient shop temperature is required when inspecting ISO 286 micron tolerances?
Under ISO 1 and NIST metrology standards, all ISO 286 limit deviations are defined at a standard reference temperature of 20°C (68°F); a 10°C temperature rise in a 50 mm steel shaft expands its diameter by +5.8 μm, consuming nearly half of an IT6 tolerance band.