Designing interfaces between prototype parts can be challenging. You should never 3D print a design with threads! Instead, you should use threaded inserts!
In general, threaded inserts are used when the material you are working with is not conducive to being tapped, and most likely that it is too soft to interface with the metal threads of a screw. McMaster shows a lot of important information, such as the “max. The holes designed into the part should be made to match the “maximum hole diameter” spec listed on McMaster.
There are 3 types of inserts that are most common:
Heat-set inserts are designed to be used with plastics. They have a textured surface designed to maximize the surface area in contact with the plastic and prevent rip-out or pullout.
These can be installed using a soldering iron as shown in the picture below:
