This is a simple thread protector that I drew up quickly for my Atlas Craftsman 618 lathe, although it should work for any lathe with 1"-10 spindle. It is intended to protect the threads from chips, dirt and dust. I usually just use a faceplate for this purpose, but unfortunately the Atlas faceplate will not allow my collet chuck to seat properly. The thread protector solves this problem.

For me, this is a temporary solution - eventually I plan to make one out of aluminum. There are some small ridges meant to secure into the threads - they seem to do a good job, but i've not really used enough to attest to the robustness. It starts kind of wonky but if you keep turning, it will snug up firmly.

I printed at a high infill density (60%) for mechanical strength and layer thickness of 0.15mm. No support enabled. In Cura i had to blow up by 2540% from the attached .stl file. The major diameter on the hex should be 1.75 inches (44.45mm).