How frequently do you have these close-tolerance parts manufactured? Do you have the option of developing a relationship with one specific manufacturer? My advice would be to have compatible software between yourself and them – then you can transfer the native design file without the need for exporting into a standard file format like STEP. If you’re using one of the big, common software packages like Solidworks or Inventor, you should be able to find someone you can work with quite easily.

The STEP file standard (ISO 10393) has a version to cater to exactly this (and more). The STEP application protocol AP242 (since 2020) includes GD&T data. You may need to buy a plugin for your design software to be able to export in it (for instance, for Solidworks, you need the MBD model-based definition package).

When you’re considering a potential manufacturer, make it clear that you will only provide the STEP file in AP242—that will help you select the right level of supplier to work with.