ISO 286 tolerances.
Enter the nominal dimension and the designation, for example H7 or g6, and obtain the limit sizes and the tolerance interval.
Open the tolerance calculatorTolerances
Manufacturing tolerances.
What each process achieves without asking for anything, how far it can be refined, and how much it costs to refine it. With the ISO 2768 table and the ISO 286 calculators.
01 / To scale
Standard tolerance is already fine.
Refining it increases cost.
A hair, an IT7 tolerance, and a micron, in cross-section and at the same scale.
What each process achieves- Human hair
- 70µm
- IT7 tolerance · Ø25 mm
- 21µm
- One micron
- 1µm
- Not specified · ISO 2768-f
- ±0.10mm
It fits three times in a hair.
One-thousandth of a millimeter.
Included in all parts. Sufficient for almost everything.
IT7 on
02 / By process
What each process achieves
and how far it can be refined.
Without requesting anything, each part comes with a general tolerance. Refining is possible, but it incurs extra costs: specify it only for the dimensions that require it.
| Process | Without specifying anything | How far refinement can go | What is advisable to specify |
|---|---|---|---|
| CNC machining | ISO 2768-f for metals and ISO 2768-m for plastics: ±0.10 mm on a 25 mm metal dimension. | IT7 for metals (21 µm on Ø25) and IT11 for plastics, on specific dimensions. Surface roughness up to Ra 1.6 µm. | Only the functional dimensions, on the PDF drawing; the rest stays under the general tolerance and keeps the price down. |
| 3D printing MJF | ±0.3 mm on dimensions up to 100 mm and ±0.3% above: ±0.6 mm on 200 mm. | A subsequent drilling or reaming for holes that fit with pins or shafts. | The dimensions that mate with another part, so we can review them before manufacturing. |
| Sheet metal cutting and bending | The cut contour and the already bent part have different precisions; the general tolerance is checked against the geometry. | What each metal, thickness and bending sequence allows; confirmed when preparing the quote. | Dimensions and angles that affect assembly, in the drawing. |
| Vacuum casting | They depend on the dimensions, geometry, resin, and shrinkage during curing. | It is checked when reviewing the design. Visual similarity to an injection-molded part does not guarantee its precision. | Functional dimensions and their requirements when requesting a quote. |
03 / General tolerances
ISO 2768:
the table that applies automatically.
The standard sets, by measurement ranges, the permissible deviation when the drawing indicates nothing.
| Nominal dimension (mm) | Class f · fine | Class m · medium |
|---|---|---|
| 0,5 a 3 | ±0,05 | ±0,1 |
| more than 3 to 6 | ±0,05 | ±0,1 |
| more than 6 to 30 | ±0,1 | ±0,2 |
| more than 30 to 120 | ±0,15 | ±0,3 |
| more than 120 to 400 | ±0,2 | ±0,5 |
| more than 400 to 1.000 | ±0,3 | ±0,8 |
| more than 1,000 to 2,000 | ±0,5 | ±1,2 |
General tolerances for linear dimensions according to ISO 2768-1. If the drawing does not specify otherwise, Proto&Go! applies class f for metals and class m for plastics, which expand and absorb moisture.
04 / When to tighten
Four rules
for requesting tolerances.
The same ones our engineering team applies when reviewing a drawing.
Only where necessary
A bearing seat, a shaft turning in a bushing or a guide needs a tight tolerance. A housing, a bracket or a clearance hole doesn't: the general tolerance is already fine.
Each grade costs
A tighter tolerance requires slower finishing passes, more careful measurement, and more rejected parts. That is why it costs money, and that is why it is advisable to reserve it.
Plastics are not metals
They expand with temperature and absorb moisture. Asking for the precision of a metal makes the part more expensive and does not guarantee the fit once assembled.
Finishes have thickness too
Anodizing adds 2.5 to 12.5 µm per face, painting up to 100 µm, and polishing removes material. Specify the final dimension so the finish stays within it.
05 / Tools
From IT grade
to limit sizes.
Two free calculators to convert from designation to numbers, without tables.
ISO 286 shaft-hole fits.
Combine the hole tolerance and the shaft tolerance and check if the fit results in clearance, interference, or transition.
Open the fits calculator06 / Frequently asked questions
Tolerances,
question by question.
What tolerance does a machined part have if I don't specify any?
If you do not specify tolerances, Proto&Go! applies the general ISO 2768-f tolerance for metals and ISO 2768-m for plastics. For a 25 mm dimension in metal, that means ±0.10 mm, the thickness of two sheets. This is sufficient for most functional parts, housings, supports, and prototypes.
Why does a tight tolerance increase the cost of a CNC part?
A tighter tolerance than the general one requires slower finishing passes, more careful measurement, and more rejected parts. That is why it is best reserved for dimensions that truly need it, such as a bearing housing. For the rest, the general tolerance is already very fine and keeps the price low.
What maximum precision can be achieved with CNC machining?
For specific functional dimensions, Proto&Go! can reach an IT7 quality in metals, about 21 microns for a 25 mm dimension, and IT11 for plastics. Plastics expand and absorb moisture, so it is not advisable to demand metal-level precision. If a part needs such a fit, mention it to the engineering team when requesting the quote.
What surface roughness does CNC machining leave?
A machined part shows fine tool marks. At Proto&Go!, surfaces up to Ra 1.6 µm are achieved, about forty times finer than a hair. If you are looking for a uniform appearance, sandblasting or anodizing masks the marks.
What tolerance do 3D printed parts have?
The Proto&Go! reference for MJF is ±0.3 mm for dimensions up to 100 mm and ±0.3% above. For a 200 mm dimension, this equates to ±0.6 mm. If a feature must fit with another part, specify the required tolerance for review before manufacturing.
What tolerance can I request for laser cutting and bending?
The precision of a cut contour and that of an already bent part are different. Indicate on the drawing the dimensions and angles that affect assembly. The team confirms their feasibility when preparing the quote.
What tolerances can I request for a vacuum casting part?
The tolerances depend on the dimensions, the geometry, the resin, and the shrinkage during curing. Indicate the functional dimensions and their requirements when requesting the quote to check if the process can meet them. A visual similarity with an injection-molded part does not guarantee the same dimensional precision.
Tolerances
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STEPSLDPRTX_T / X_BIPTCATPARTPRTSAT3DM
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