> For the complete documentation index, see [llms.txt](https://monasheng.gitbook.io/zerotohero/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://monasheng.gitbook.io/zerotohero/3d-printing-zero-to-hero/advanced-skills/advanced-cad/3d-printing-tolerances-and-fits.md).

# 3D Printing Tolerances & Fits

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:man\_mage: **Important:** Like all made parts, the dimensions of your finished 3D prints are subject to uncontrollable manufacturing realities that lead to deviations from nominal dimensions.
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## Sources of tolerance

Tolerances relative to CAD arise from:

* discretisation in the [STL Export](/zerotohero/3d-printing-zero-to-hero/core-skills/stl-export.md) process,
* &#x20;settings/layer heights/paths planned for the 3D printer when [Slicing](/zerotohero/3d-printing-zero-to-hero/core-skills/slicing.md),
* physical limitations of the printer, including backlash, temperature variations, misalignment, out-of-level, etc, and,
* shrinkage of your parts as they cool.

Particularly with respect to physical limitations, the final tolerance you achieve can be a function of the specific printer and filament you use, and potentially even the day you use it on. If you want to achieve high dimensional accuracy, some level of characterisation/tuning/trial and error will almost certainly be required!

## General Guidelines

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:man\_mage: **Important:** The follow general guidelines may help you narrow-in on a desired tolerance for your parts:

* $$0.20-0.15;\text{mm}$$ of clearance between mating parts will require a great deal of force to put together and will be very difficult to separate,
* $$0.25;\text{mm}$$ of clearance will provide parts that fit together snugly with minimal force, and,
* $$\geq0.35;\text{mm}$$ larger clearance will generally produce a loose fit.
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In cases where your parts are too small to fit together, you can remedy this with sandpaper, a drill, or a heat gun.

For dimension-critical holes, you might intentionally elect to print undersize and then drill/ream.