Mechanical Engineering

kinda depends on the machine and the person operating it...

that also :)

Also tolerance depends on material and temperature at which the part will be made. Nontheless, there are some factors that don't depend on machining directly - like working temperature and purpose of the part (maybe not necessarily to achieve such close parameters). So the question has a large number of answers.

Depend on the standard you are using, there are tolerance guides available on the internet for various clearances including the machining class

https://www.bossard.com/au-en/assembly-technology-expert/technical-information-and-tools/technical-information/general-tolerances-tables-standards/basic-tolerances-and-tolerance-fields/

As previously discussed, what is achievable is process and material dependant. I like using the machinist's handbook as a quick reference on my desk. Would highly recommend getting one if you dont have it, if i stick with that then the machinist rarely complains... not to say some extremely tight tolerances aren't achievable. But tighter tolerances cost more.

As a rough guide

Aerospace±0.001 mm to ±0.005 mm

Medical Devices±0.001 mm to ±0.01 mm

Automotive±0.01 mm to ±0.05 mm

Depends on material, hardening and temperature

the real question is not about the most precise tolerance, BUT how cost efficent the proces is.

With long polishing you can get single microns, yet do you really need it so precise?