When designing built-in THREADS, avoid sharp edges and include a radius on the root. Also, use a “dog point” head of at least 0.8 mm, this makes starting the thread much easier. Small threads, smaller than 8…10 mm, are not recommended and hand-tapping probably required to smooth threads and correct clearances. Easy alternative is to make holes smaller than required for the thread, and drill and tap thread, or use self-tapping threaded inserts. Lock nuts, embedded nuts, or metal inserts are stronger fastening options than adding threads to the FDM plastic.