ISO H7 Tolerance Chart for Bore Dimensions: (Full Table)

Atishay Jain · March 21, 2026 · 3 min read

H7 is the most common ISO fit class on aerospace and precision engineering drawings. If you machine bores for European OEMs, you will encounter H7 more often than any other fit designation.

This ISO H7 tolerance chart for bore dimensions gives you every lookup value you need, from 3mm to 100mm, with worked examples and FAI formatting guidance.

Unlike G6 (where the bore is always above nominal), H7 starts at exactly the nominal size and goes up.

ISO H7 Tolerance Chart for Bore Dimensions: The Lookup Table

H7 means: fundamental deviation H (lower deviation = 0, bore starts at nominal size) with IT7 tolerance grade.

Nominal Bore	Lower Dev.	IT7 Grade	Upper Dev.	Lower Limit	Upper Limit	Total Band
3 mm	0	0.010	+0.010	3.000	3.010	10 um
5 mm	0	0.012	+0.012	5.000	5.012	12 um
6 mm	0	0.012	+0.012	6.000	6.012	12 um
8 mm	0	0.015	+0.015	8.000	8.015	15 um
10 mm	0	0.015	+0.015	10.000	10.015	15 um
12 mm	0	0.018	+0.018	12.000	12.018	18 um
15 mm	0	0.018	+0.018	15.000	15.018	18 um
18 mm	0	0.018	+0.018	18.000	18.018	18 um
20 mm	0	0.021	+0.021	20.000	20.021	21 um
25 mm	0	0.021	+0.021	25.000	25.021	21 um
30 mm	0	0.021	+0.021	30.000	30.021	21 um
40 mm	0	0.025	+0.025	40.000	40.025	25 um
50 mm	0	0.025	+0.025	50.000	50.025	25 um
60 mm	0	0.030	+0.030	60.000	60.030	30 um
80 mm	0	0.030	+0.030	80.000	80.030	30 um
100 mm	0	0.035	+0.035	100.000	100.035	35 um

Key characteristic of H7: The lower limit always equals the nominal size exactly. A 20mm H7 bore must be at least 20.000mm. A bore that measures 19.998mm is out of tolerance on the low side.

H7 IS A LOOKUP. YOUR WHOLE DRAWING ISN'T

You can look up one H7 bore in a chart. Mavlon resolves every fit, tolerance, and dimension on the drawing at once.

Bring your hardest drawing. Watch it become a Form 3 live.

Worked Example: 25mm H7

Nominal: 25.000mm
Size range: over 18mm to 30mm
Fundamental deviation H: 0 (lower limit = nominal)
IT7 for this range: 0.021mm
Lower limit: 25.000mm
Upper limit: 25.000 + 0.021 = 25.021mm
Total tolerance band: 21 microns

H7 vs G6: When to Use Each

Aspect	H7	G6
Bore position relative to nominal	Starts at nominal, goes up	Starts above nominal, goes further up
Typical application	General precision fit (pin/shaft mating)	Clearance fit (bearing housing, bushing seat)
Manufacturing	Reaming achievable for most sizes	Honing often required for small bores
Tolerance band at 10mm	15 um	9 um (tighter)

H7 is more forgiving than G6 because the tolerance band is wider (IT7 vs IT6). A 10mm H7 bore has a 15-micron window; a 10mm G6 bore has only a 9-micron window.

FAI Row Format for H7

Field	Value
Requirement	25.0 H7 +0.021/0 mm
Nominal	25.0
Tol +	0.021
Tol -	0.000
Upper Limit	25.021
Lower Limit	25.000
Inspection Method	Inside micrometer / Bore gauge
Notes	[ISO fit class H7 expanded]

Manufacturing H7 Bores

H7 is achievable with precision reaming for most bore sizes. Unlike G6 (which often requires honing), a quality carbide reamer in a rigid setup can hold the H7 band on aluminum and most steels.

Recommended process:

Drill undersize (1 to 2mm under nominal)
Semi-finish bore or rough ream to within 0.05mm of nominal
Finish ream with precision reamer to final size
Verify with bore gauge or air gauge

For larger bores (above 40mm), boring on the CNC mill with a precision boring head is often more practical than reaming.

Modern drawing ballooning software expands fit classes like H7 to these limits automatically when building a characteristic list.

Mavlon Expands H7 and All ISO Fit Classes Automatically

Mavlon recognizes H7, G6, H6, f7, g6, and all other ISO fit class callouts.

It expands each one to actual upper and lower limits based on the nominal diameter and the ISO 286 tables, then formats the result as a ready-to-use FAI row.

Test it on your drawing. Not a sample. Yours.