Having the PDF is useless without interpretation. Here is a step-by-step guide to using the ISO 20457 tolerance table PDF in real-world engineering.
Step 1: Determine the functional requirement. Ask: Does this feature need to slide, press, or simply exist?
Step 2: Measure the nominal size. Find the row in the table corresponding to your part's length, width, or diameter. For a 45mm long housing, you look at the "30 up to 120" row.
Step 3: Read the deviation. Using the "Medium" class for a 45mm part, the linear tolerance is ± 0.8 mm. This means your part can be 44.2 mm to 45.8 mm. iso 20457 tolerance table pdf
Step 4: Apply to drawings. If your general tolerance block references "ISO 20457 – m", you do not need to write individual tolerances on every dimension. The machinist knows to adhere to the Medium tolerance table.
Below is a representative example of the tolerance table structure from ISO 20457 (values in mm, for general-purpose unfilled plastics):
| Nominal dimension (mm) | Tolerance grade 1 (fine) | Grade 2 (medium) | Grade 3 (coarse) | Grade 4 (very coarse) | |------------------------|--------------------------|------------------|------------------|------------------------| | 0 – 3 | ±0.05 | ±0.10 | ±0.20 | ±0.40 | | >3 – 6 | ±0.06 | ±0.12 | ±0.24 | ±0.48 | | >6 – 10 | ±0.08 | ±0.15 | ±0.30 | ±0.60 | | >10 – 18 | ±0.10 | ±0.20 | ±0.40 | ±0.80 | | >18 – 30 | ±0.12 | ±0.25 | ±0.50 | ±1.00 | | >30 – 50 | ±0.15 | ±0.30 | ±0.60 | ±1.20 | | >50 – 80 | ±0.20 | ±0.40 | ±0.80 | ±1.60 | | >80 – 120 | ±0.25 | ±0.50 | ±1.00 | ±2.00 | | >120 – 180 | ±0.30 | ±0.60 | ±1.20 | ±2.40 | | >180 – 250 | ±0.40 | ±0.80 | ±1.60 | ±3.20 | Having the PDF is useless without interpretation
Note: Actual values in the official standard vary by material (e.g., glass-filled, amorphous, crystalline). The above is an illustrative summary.
The standard provides tolerance tables categorized by the Type of Dimension and the Material Group.
Even with the PDF in hand, errors happen. Avoid these pitfalls: Step 2: Measure the nominal size
The standard uses a letter-number combination to define tolerance grades:
In practice, ISO 20457 defines tolerance tables based on: