This reference provides the complete IT grade tolerance tables per ISO 286 for hole features, common fits used in hydraulic and mechanical assemblies, and the tolerance capabilities of deep hole drilling processes.
1. Complete IT Grade Table (ISO 286)
Values are in micrometers (μm) for IT1–IT11 and millimeters (mm) for IT12–IT18. For holes with fundamental deviation H, the lower deviation (EI) is zero — the hole can only be larger than nominal.
| Basic Size (mm) | IT1 | IT2 | IT3 | IT4 | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 (mm) | IT13 (mm) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| >0 – 3 | 0.8 | 1.2 | 2 | 3 | 4 | 6 | 10 | 14 | 25 | 40 | 60 | 0.10 | 0.14 |
| >3 – 6 | 1.0 | 1.5 | 2.5 | 4 | 5 | 8 | 12 | 18 | 30 | 48 | 75 | 0.12 | 0.18 |
| >6 – 10 | 1.0 | 1.5 | 2.5 | 4 | 6 | 9 | 15 | 22 | 36 | 58 | 90 | 0.15 | 0.22 |
| >10 – 18 | 1.2 | 2.0 | 3 | 5 | 8 | 11 | 18 | 27 | 43 | 70 | 110 | 0.18 | 0.27 |
| >18 – 30 | 1.5 | 2.5 | 4 | 6 | 9 | 13 | 21 | 33 | 52 | 84 | 130 | 0.21 | 0.33 |
| >30 – 50 | 1.5 | 2.5 | 4 | 7 | 11 | 16 | 25 | 39 | 62 | 100 | 160 | 0.25 | 0.39 |
| >50 – 80 | 2.0 | 3 | 5 | 8 | 13 | 19 | 30 | 46 | 74 | 120 | 190 | 0.30 | 0.46 |
| >80 – 120 | 2.5 | 4 | 6 | 10 | 15 | 22 | 35 | 54 | 87 | 140 | 220 | 0.35 | 0.54 |
| >120 – 180 | 3.5 | 5 | 8 | 12 | 18 | 25 | 40 | 63 | 100 | 160 | 250 | 0.40 | 0.63 |
| >180 – 250 | 4.5 | 7 | 10 | 14 | 20 | 29 | 46 | 72 | 115 | 185 | 290 | 0.46 | 0.72 |
| >250 – 315 | 6.0 | 8 | 12 | 16 | 23 | 32 | 52 | 81 | 130 | 210 | 320 | 0.52 | 0.81 |
| >315 – 400 | 7.0 | 9 | 13 | 18 | 25 | 36 | 57 | 89 | 140 | 230 | 360 | 0.57 | 0.89 |
| >400 – 500 | 8.0 | 10 | 15 | 20 | 27 | 40 | 63 | 97 | 155 | 250 | 400 | 0.63 | 0.97 |
| >500 – 630 | 9.0 | 11 | 16 | 22 | 32 | 44 | 70 | 110 | 175 | 280 | 440 | 0.70 | 1.10 |
| >630 – 800 | 10 | 13 | 18 | 25 | 36 | 50 | 80 | 125 | 200 | 320 | 500 | 0.80 | 1.25 |
| >800 – 1000 | 11 | 15 | 21 | 28 | 40 | 56 | 90 | 140 | 230 | 360 | 560 | 0.90 | 1.40 |
Sources: ISO 286-2; RoyMech ISO tolerance tables; Schaeffler ISO tolerances; Engineers Edge ISO 286; Bossard tolerance fields.
2. Common Hole Basis Fits
In the hole-basis system (preferred for manufacturing), the hole is H-grade and the shaft letter determines the fit type.
| Fit Type | Typical Hole | Typical Shaft | Application Example |
|---|---|---|---|
| Loose running | H11 | c11 | Exposed clearance, wide temp variation |
| Free running | H9 | d9 | General machinery, moderate clearance |
| Easy running | H8 | f7 | Precision spindles, oil-lubricated |
| Sliding | H7 | g6 | Precise sliding, no noticeable play |
| Close clearance | H7 | h6 | Locating fits, can be assembled by hand |
| Light interference | H7 | k6 | Press fit for thin sections, can be disassembled |
| Medium interference | H7 | n6 | Normal press fit, needs force |
| Heavy interference | H7 | s6 | Permanent press fit, high interference |
| Force | H7 | u6 | Very heavy press, extreme interference |
Source: ISO 286; Tungaloy catalog.
3. Tolerance Capability by Manufacturing Process
| Process | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 | IT13 |
|---|---|---|---|---|---|---|---|---|---|
| Lapping | ✅ | ✅ | |||||||
| Honing | ✅ | ✅ | |||||||
| Cylindrical grinding | ✅ | ✅ | |||||||
| Reaming | ✅ | ✅ | ✅ | ||||||
| Gun drilling | ✅ | ✅ | ✅ | ||||||
| BTA drilling (fine boring) | ✅ | ✅ | |||||||
| BTA drilling (standard) | ✅ | ✅ | |||||||
| Ejector drilling | ✅ | ✅ | |||||||
| Boring / turning | ✅ | ✅ | ✅ | ✅ | ✅ | ||||
| Milling | ✅ | ✅ | ✅ | ✅ | |||||
| Trepanning | ✅ | ✅ | |||||||
| Conventional drilling | ✅ | ✅ | ✅ | ||||||
| Die casting | ✅ | ✅ | ✅ |
Sources: Tungaloy catalog; ISCAR Drilling Handbook; Ingersoll gundrill specs.
4. Tolerance Example — 50 mm Bore by Method
| Method | Achievable IT | Tolerance Band | 50 mm Bore Limits |
|---|---|---|---|
| Lapping / Honing | IT5–IT6 | 13–19 μm | 50.000–50.019 mm |
| Gun drilling (optimized) | IT7 | 25 μm | 50.000–50.025 mm |
| Gun drilling (standard) | IT8 | 39 μm | 50.000–50.039 mm |
| BTA drilling (fine boring) | IT7–IT8 | 25–39 μm | 50.000–50.039 mm |
| BTA drilling (standard) | IT9–IT10 | 62–100 μm | 50.000–50.100 mm |
| Ejector drilling | IT10–IT11 | 100–160 μm | 50.000–50.160 mm |
| Reaming | IT7–IT8 | 25–39 μm | 50.000–50.039 mm |
| Skiving & roller burnishing | IT8 (H8) | 39 μm | 50.000–50.039 mm |
5. H7 Tolerances (Most Common Precision Fit) by Diameter
| Diameter Range (mm) | H7 Tolerance (μm) | Limits (mm) |
|---|---|---|
| 0–3 | +10 / 0 | 0.000–0.010 |
| 3–6 | +12 / 0 | 0.000–0.012 |
| 6–10 | +15 / 0 | 0.000–0.015 |
| 10–18 | +18 / 0 | 0.000–0.018 |
| 18–30 | +21 / 0 | 0.000–0.021 |
| 30–50 | +25 / 0 | 0.000–0.025 |
| 50–80 | +30 / 0 | 0.000–0.030 |
| 80–120 | +35 / 0 | 0.000–0.035 |
| 120–180 | +40 / 0 | 0.000–0.040 |
| 180–250 | +46 / 0 | 0.000–0.046 |
| 250–315 | +52 / 0 | 0.000–0.052 |
6. H8 Tolerances (Hydraulic Cylinder Standard) by Diameter
| Diameter Range (mm) | H8 Tolerance (μm) | Limits (mm) |
|---|---|---|
| 0–3 | +14 / 0 | 0.000–0.014 |
| 3–6 | +18 / 0 | 0.000–0.018 |
| 6–10 | +22 / 0 | 0.000–0.022 |
| 10–18 | +27 / 0 | 0.000–0.027 |
| 18–30 | +33 / 0 | 0.000–0.033 |
| 30–50 | +39 / 0 | 0.000–0.039 |
| 50–80 | +46 / 0 | 0.000–0.046 |
| 80–120 | +54 / 0 | 0.000–0.054 |
| 120–180 | +63 / 0 | 0.000–0.063 |
| 180–250 | +72 / 0 | 0.000–0.072 |
Key Sources
- ISO 286-2:2010, “Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes — Tables of standard tolerance classes and limit deviations for holes and shafts”
- RoyMech, “ISO 286 Hole Tolerances” — complete tolerance tables up to 3,150 mm
- Schaeffler, “ISO Tolerances” — bearing fit recommendations
- Engineers Edge, “ISO Tolerances for Bolt Fastener and Holes Table Chart ISO 286”
- Tungaloy catalog (p. 1052) — IT grade table and process capability matrix
- Ingersoll Cutting Tools, “Brazed Gundrills” — gun drilling IT grade specifications
- ISCAR Drilling Handbook — BTA and ejector drilling IT grades