Tolerances & Fits
Standard ISO tolerance grades (IT) and preferred fits let you specify locators, bushings and pins clearly and interchangeably. The values below are nominal ISO data.
ISO Tolerance Grades IT5 – IT12 (µm)
Tolerance magnitude for a given nominal size range and grade. Smaller IT = tighter tolerance. Fixture locating surfaces typically use IT5–IT7; general machining IT9–IT11.
| Nominal range (mm) | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 |
|---|---|---|---|---|---|---|---|---|
| up to 3 | 4 | 6 | 10 | 14 | 25 | 40 | 60 | 100 |
| >3 – 6 | 5 | 8 | 12 | 18 | 30 | 48 | 75 | 120 |
| >6 – 10 | 6 | 9 | 15 | 22 | 36 | 58 | 90 | 150 |
| >10 – 18 | 8 | 11 | 18 | 27 | 43 | 70 | 110 | 180 |
| >18 – 30 | 9 | 13 | 21 | 33 | 52 | 84 | 130 | 210 |
| >30 – 50 | 11 | 16 | 25 | 39 | 62 | 100 | 160 | 250 |
| >50 – 80 | 13 | 19 | 30 | 46 | 74 | 120 | 190 | 300 |
| >80 – 120 | 15 | 22 | 35 | 54 | 87 | 140 | 220 | 350 |
| >120 – 180 | 18 | 25 | 40 | 63 | 100 | 160 | 250 | 400 |
| >180 – 250 | 20 | 29 | 46 | 72 | 115 | 185 | 290 | 460 |
Preferred Fits (Hole Basis)
| Fit | Type | Typical use |
|---|---|---|
| H7/g6 | Clearance (slide) | Sliding locator pins, renewable bushings |
| H7/f7 | Clearance (loose running) | Free-running parts |
| H7/h6 | Clearance (locating) | Precise sliding, gauge fits |
| H7/js6 | Transition | Light press / adjustable locating |
| H7/k6 | Transition | Locating pins in body (light press) |
| H7/m6 | Transition | Dowel pins, fixed bushings |
| H7/p6 | Interference (light press) | Press-fit bushings in steel |
| H7/r6 | Interference | Press-fit bushings in cast iron / heavier press |
| H7/s6 | Interference (heavy press) | Permanent assemblies |
Recommended Fits for Fixture Components
| Component joint | Recommended fit |
|---|---|
| Jig bushing into liner / body | H7/p6 (steel body), H7/r6 (cast iron body) |
| Renewable bushing into liner | H7/g6; H6/g5 for high precision |
| Locator pin into body | H7/js6 or H7/k6 |
| Diamond pin into body | H7/js6 |
| Dowel pin into body | H7/m6 or H7/n6 |
| T-slot bolt in T-slot | Clearance per T-slot standard (H12 style) |
Surface Roughness by Process
| Process | Ra (µm) |
|---|---|
| Lapping / polishing | 0.05 – 0.2 |
| Grinding (finish) | 0.2 – 0.8 |
| Reaming | 0.8 – 1.6 |
| Boring | 0.8 – 3.2 |
| Milling (fine) | 1.6 – 6.3 |
| Turning (finish) | 1.6 – 6.3 |
| Drilling | 6.3 – 12.5 |
| Sawing / roughing | 12.5 – 50 |
General Tolerances (ISO 2768-mK)
When no specific tolerance is given: linear dimensions ±0.1 mm for ≤10 mm, ±0.2 for 10–30 mm, ±0.3 for 30–120 mm, ±0.5 for 120–400 mm; angles ±0.5°; flatness/straightness 0.2 mm. Override with explicit tolerances on critical features.
Hole-Basis System (H)
Hole H is the basic element; the shaft letter sets the fit — g/h clearance, k/m/n transition, p/r/s interference.
Shaft-Basis System (h)
Shaft h is the basic element; the hole letter sets the fit — G/H clearance, K transition, P/R interference.
Fit Types in Cross-Section
IT Grades (µm, 30–50 mm range)
Higher IT number = looser tolerance. Locating surfaces use IT5–IT7; general machining IT9–IT11.