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 ...

If you do much practical 3D printing, you eventually need some sort of fastener. You can use a screw to bite into plastic. You can create a clearance hole to accommodate a bolt and a nut or even build ...