What is an H7/g6 fit used for?

H7/g6 is a clearance fit used for moving parts that need precise sliding motion without binding — locating pins, lightly-loaded bearing journals on shafts, sliding gears, and clamp screws. The minimum clearance is small but positive across the full diameter range, and the maximum clearance is small enough to keep wobble under control. Typical applications: gauge pins running in gauge bushings, light-load shafts in machine spindles, and indexing dowels.

What is the difference between H7/h6 and H7/g6?

H7/h6 is a locational clearance fit with zero minimum clearance — the shaft and hole can be the same size at the worst case (shaft at upper limit, hole at lower limit). H7/g6 has a small guaranteed minimum clearance because the shaft tolerance band sits entirely below the nominal. Use H7/h6 when the parts are stationary in service (assembled and not moving relative to each other). Use H7/g6 when sliding motion is required and even occasional binding is unacceptable.

What is an H7/p6 fit?

H7/p6 is a light interference (press) fit where the shaft is slightly larger than the hole, producing 0 to 30+ μm of interference depending on size. Used for permanent assemblies where the parts should not move relative to each other but can still be assembled with an arbor press at room temperature. Common for bearing inner rings on shafts, dowel pins, valve seats, and bushings. Heavier interferences (r6, s6, u6) require heating or freezing one part for assembly.

When do I use hole-basis vs shaft-basis?

Hole-basis (H7/something) is the default for most manufacturing because holes are produced by reaming and broaching with fixed tooling — making holes to a standard size (H7) and varying the shaft is cheaper than the reverse. Shaft-basis (something/h6) is used when the shaft is purchased to a standard size from a vendor (commodity shafting, bar stock, dowel pins) and the hole is produced to a varying tolerance. About 80% of engineering drawings use hole-basis.

How accurate is an IT7 tolerance?

IT7 is the standard precision-machining tolerance grade per ISO 286. For a 25 mm feature, IT7 = 21 μm; for 50 mm, IT7 = 25 μm; for 100 mm, IT7 = 35 μm. IT7 is achievable by reaming, fine boring, or grinding. The next tighter grade IT6 (typically 16 μm at 25 mm) requires precision grinding or honing. IT8 (33 μm at 25 mm) is achievable by turning or rough grinding. IT11 (130 μm at 25 mm) is rough machining.

ISO 286 fits chart: hole-basis and shaft-basis tolerance reference.

Fits Reference ISO 286-1:2010 / ISO 286-2:2010 Updated May 2026

Complete reference for ISO 286 hole-basis and shaft-basis fits. Tolerance values for IT6, IT7, IT8 in common diameter ranges. Worst-case clearance and interference for every standard fit class — H7/g6 (sliding), H7/h6 (locational clearance), H7/k6 (transition), H7/n6 (light interference), H7/p6 (press), H7/r6 / H7/s6 / H7/u6 (medium and heavy interference).

The three fit categories

Every ISO 286 fit falls into one of three categories based on the worst-case relationship between hole and shaft size:

Clearance fit. Minimum clearance ≥ 0 across all conditions. Examples: H7/d9 (loose running), H7/f7 (close running), H7/g6 (sliding), H7/h6 (locational clearance).
Transition fit. Can be either clearance or interference depending on the actual sizes within tolerance. Examples: H7/j6 (slight clearance to slight interference), H7/k6 (slight interference at upper limits), H7/n6 (small interference).
Interference fit. Maximum clearance ≤ 0 across all conditions; the shaft is always larger than the hole. Examples: H7/p6 (light press), H7/r6 (medium press), H7/s6 (heavy press), H7/u6 (force fit).

The standard fits

Hole-basis common fits — by application

Fit	Type	Typical use
H11/c11	Clearance (loose)	Agricultural assembly, large-clearance pins
H9/d9	Clearance (free running)	Pulleys, idler gears, loose-fit bushings
H8/f7	Clearance (close running)	Light-duty journal bearings, sleeve bearings
H7/g6	Clearance (sliding)	Sliding pins, indexing dowels, gauge pins in bushings
H7/h6	Clearance (locational)	Precise location, no movement, easy assembly
H7/j6	Transition (push)	Hand-press assembly, slight clearance or slight interference
H7/k6	Transition (light keying)	Mallet-fit, can be disassembled, keys against rotation
H7/n6	Transition (medium drive)	Permanent location with mallet or light press
H7/p6	Interference (light press)	Bearing rings on shafts (small bearings), dowel pins
H7/r6	Interference (medium press)	Hub-on-shaft, bushing in housing (steel-on-steel)
H7/s6	Interference (heavy press)	Permanent assembly, bearing inner ring on shaft (medium)
H7/u6	Interference (force/shrink)	Heat or freeze required for assembly, locomotive wheels

Hole tolerance — H6, H7, H8 grades by diameter range

Hole tolerance values per ISO 286-2. Upper deviation = +IT, lower deviation = 0. All values in μm.

Diameter (mm)	H6 (+μm)	H7 (+μm)	H8 (+μm)	H9 (+μm)	H11 (+μm)
over 3 to 6	8	12	18	30	75
over 6 to 10	9	15	22	36	90
over 10 to 18	11	18	27	43	110
over 18 to 30	13	21	33	52	130
over 30 to 50	16	25	39	62	160
over 50 to 80	19	30	46	74	190
over 80 to 120	22	35	54	87	220
over 120 to 180	25	40	63	100	250
over 180 to 250	29	46	72	115	290
over 250 to 315	32	52	81	130	320
over 315 to 400	36	57	89	140	360
over 400 to 500	40	63	97	155	400

Example: a 30 mm H7 hole = 30.000 to 30.021 mm. The hole tolerance band is always above the nominal.

Shaft tolerance — common grades by diameter range

Shaft tolerance values per ISO 286-1. All values in μm. Format: upper / lower deviation.

Diameter (mm)	g6	h6	j6	k6	n6	p6	r6	s6
over 3 to 6	−4/−12	0/−8	+6/−2	+9/+1	+16/+8	+20/+12	+23/+15	+27/+19
over 6 to 10	−5/−14	0/−9	+7/−2	+10/+1	+19/+10	+24/+15	+28/+19	+32/+23
over 10 to 18	−6/−17	0/−11	+8/−3	+12/+1	+23/+12	+29/+18	+34/+23	+39/+28
over 18 to 30	−7/−20	0/−13	+9/−4	+15/+2	+28/+15	+35/+22	+41/+28	+48/+35
over 30 to 50	−9/−25	0/−16	+11/−5	+18/+2	+33/+17	+42/+26	+50/+34	+59/+43
over 50 to 65	−10/−29	0/−19	+12/−7	+21/+2	+39/+20	+51/+32	+60/+41	+72/+53
over 65 to 80	−10/−29	0/−19	+12/−7	+21/+2	+39/+20	+51/+32	+62/+43	+78/+59
over 80 to 100	−12/−34	0/−22	+13/−9	+25/+3	+45/+23	+59/+37	+73/+51	+93/+71
over 100 to 120	−12/−34	0/−22	+13/−9	+25/+3	+45/+23	+59/+37	+76/+54	+101/+79
over 120 to 140	−14/−39	0/−25	+14/−11	+28/+3	+52/+27	+68/+43	+88/+63	+117/+92
over 140 to 160	−14/−39	0/−25	+14/−11	+28/+3	+52/+27	+68/+43	+90/+65	+125/+100
over 160 to 180	−14/−39	0/−25	+14/−11	+28/+3	+52/+27	+68/+43	+93/+68	+133/+108
over 180 to 200	−15/−44	0/−29	+16/−13	+33/+4	+60/+31	+79/+50	+106/+77	+151/+122

Worst-case clearance/interference — common fits at 25 mm nominal

For a 25 mm diameter (in the 18–30 mm tolerance band), the clearance or interference for the most-used fits:

Fit	Hole limits (mm)	Shaft limits (mm)	Max clearance / Min interference	Min clearance / Max interference
H7/g6	25.000 / 25.021	24.980 / 24.993	0.041 clearance	0.007 clearance
H7/h6	25.000 / 25.021	24.987 / 25.000	0.034 clearance	0.000 (line-to-line)
H7/j6	25.000 / 25.021	24.996 / 25.009	0.025 clearance	0.009 interference
H7/k6	25.000 / 25.021	25.002 / 25.015	0.019 clearance	0.015 interference
H7/n6	25.000 / 25.021	25.015 / 25.028	0.006 clearance	0.028 interference
H7/p6	25.000 / 25.021	25.022 / 25.035	0.001 interference	0.035 interference
H7/r6	25.000 / 25.021	25.028 / 25.041	0.007 interference	0.041 interference
H7/s6	25.000 / 25.021	25.035 / 25.048	0.014 interference	0.048 interference

Positive value = clearance (shaft smaller than hole). Negative value = interference (shaft larger than hole, force-fit required).

Standard IT grades — tolerance magnitude by diameter

IT grades define the magnitude of the tolerance band, regardless of where it sits relative to the nominal. Used as the "6" or "7" in callouts like H7 or h6.

Diameter (mm)	IT5	IT6	IT7	IT8	IT9	IT11
over 3 to 6	5	8	12	18	30	75
over 6 to 10	6	9	15	22	36	90
over 10 to 18	8	11	18	27	43	110
over 18 to 30	9	13	21	33	52	130
over 30 to 50	11	16	25	39	62	160
over 50 to 80	13	19	30	46	74	190
over 80 to 120	15	22	35	54	87	220
over 120 to 180	18	25	40	63	100	250
over 180 to 250	20	29	46	72	115	290
over 250 to 315	23	32	52	81	130	320
over 315 to 400	25	36	57	89	140	360
over 400 to 500	27	40	63	97	155	400

Values in μm. Reference: ISO 286-1 Table 1.

Achievable IT grades — by manufacturing process

Process	Typical IT grade	Best IT grade
Lapping, honing	IT3–IT5	IT1
Cylindrical / surface grinding	IT5–IT7	IT4
Fine boring / fine turning	IT6–IT8	IT5
Reaming	IT7–IT9	IT6
Turning (normal)	IT8–IT10	IT7
Milling	IT9–IT11	IT8
Drilling	IT10–IT13	IT9
Broaching	IT7–IT9	IT6
Stamping	IT11–IT13	IT9
Sand casting	IT14–IT16	IT12
Die casting	IT11–IT13	IT9
Investment casting	IT10–IT12	IT8

Specifying tighter than needed The cost increase from IT7 to IT6 on a precision-turned feature is typically 2–3×. From IT6 to IT5 it's another 3–4×. Always check whether the fit class actually requires the tighter grade. An H7/h6 fit at IT7 + IT6 covers most engineering applications adequately; jumping to H6/h5 doubles cost without function.

5 common fit specification mistakes

Specifying tight clearance fits for high-temperature service. A H7/g6 sliding fit at room temperature can become an interference fit at 200 °C if the shaft material has higher thermal expansion than the housing. Always account for thermal expansion when service temperature differs from assembly temperature by more than 50 °C.
Confusing H7/k6 with H7/n6. H7/k6 is a light transition fit assembled by mallet, removable with a puller. H7/n6 is a medium drive fit assembled by light press, removable with significant force. Picking the wrong one either makes assembly impossible (n6 by mallet) or assembly too loose (k6 by press).
Using interference fits without considering shaft material strength. A H7/u6 force fit on a thin-walled aluminium hub creates stresses that exceed the hub's yield strength. Always check interference-induced hoop stress with the press fit calculator before specifying.
Specifying ISO 286 fits on out-of-range diameters. ISO 286-1 covers diameters from 0 to 500 mm. For larger features, the fit codes still work but the tolerance values in the standard tables are extrapolated and less accurate. Above 500 mm use ISO 8015 general tolerances plus explicit numeric tolerances.
Choosing hole-basis when shaft is purchased. If you buy commodity shafting (ground bar stock) to standard h6 or h7, then designing a hole-basis fit forces you to grind the shaft to the H-basis specification. Use shaft-basis instead, varying the hole tolerance.

Need clearance or interference for a specific size/fit? The MetricMech ISO 286 Fits Calculator handles arbitrary diameters and fit classes, producing the worst-case clearance or interference plus the hole and shaft tolerance limits. For press-fit hoop stress and assembly force calculations, see the Press / Interference Fit Calculator.

References

ISO 286-1:2010 — Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes — Part 1: Basis of tolerances, deviations and fits
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 1829:1975 — Selection of tolerance zones for general purposes
ISO 8015:2011 — Geometrical product specifications (GPS) — Fundamentals — Concepts, principles and rules

For interactive fit selection with custom inputs, see the ISO 286 Fits Calculator. For interference-fit press force and hoop stress, see the Press Fit Calculator. For position tolerance interaction with fits, see the Position Tolerance reference.