There’s a variety of ways to add threaded holes to 3D printed objects. You can tap a hole, but the plastic isn’t always strong enough. Nut traps work, but aren’t very attractive and can be difficult ...
Hackaday

threaded insert

Sometimes, when making a 3D printed object, plastic just isn’t enough. Probably the most common addition to our prints is the ubiquitous brass threaded inset, which has proven its worth time and again ...
A high strength hexagonal insert has been developed that is ideal for use in high volume hydro-formed parts, including plastics and composites. Dean Palmer reports In the drive to reduce weight, many ...