ISO Fits & Tolerances
Standard hole and shaft basis fits for precision mechanical design
Common Hole Basis Fits (ISO)
| Fit Type | Hole | Shaft | Description | Application |
|---|---|---|---|---|
| Loose Running | H11 | c11 | Large clearance | Pivots, latches |
| Free Running | H9 | d9 | Wide clearance | Bearings, gears on shafts |
| Close Running | H8 | f7 | Small clearance | Precision spindles |
| Sliding | H7 | g6 | Minimal clearance | Accurate slides, spigots |
| Locational Clearance | H7 | h6 | Zero to slight clearance | Stationary locating fits |
| Locational Transition | H7 | k6 | Slight interference or clearance | Accurate location, light press |
| Locational Transition | H7 | n6 | More interference | Press fit, light drive |
| Locational Interference | H7 | p6 | Light press fit | Permanent assembly |
| Medium Drive | H7 | r6 | Medium press fit | Bronze bushings |
| Force Fit | H7 | s6 | Heavy press fit | Permanent assembly, no key |
ISO Tolerance Grades (IT)
| Grade | Application | Typical Process |
|---|---|---|
| IT01-IT1 | Gauge blocks, master gauges | Lapping, honing |
| IT2-IT4 | Precision gauges, instruments | Grinding, lapping |
| IT5-IT6 | Precision fits, bearings | Grinding, precision turning |
| IT7 | High quality fits | Turning, boring, milling |
| IT8-IT9 | General engineering | Standard machining |
| IT10-IT11 | Non-critical dimensions | Drilling, rough machining |
| IT12-IT16 | Rough work, castings | Sawing, flame cutting |
Tolerance Values (IT7) - Selected Sizes
| Basic Size (mm) | IT6 (μm) | IT7 (μm) | IT8 (μm) | IT9 (μm) |
|---|---|---|---|---|
| 1-3 | 6 | 10 | 14 | 25 |
| 3-6 | 8 | 12 | 18 | 30 |
| 6-10 | 9 | 15 | 22 | 36 |
| 10-18 | 11 | 18 | 27 | 43 |
| 18-30 | 13 | 21 | 33 | 52 |
| 30-50 | 16 | 25 | 39 | 62 |
| 50-80 | 19 | 30 | 46 | 74 |
| 80-120 | 22 | 35 | 54 | 87 |
| 120-180 | 25 | 40 | 63 | 100 |
| 180-250 | 29 | 46 | 72 | 115 |
Shaft Fundamental Deviations
a-h: Shafts smaller than hole (clearance fits)
j-n: Transition fits (may have clearance or interference)
p-z: Shafts larger than hole (interference fits)