A simple M40 lock nut, with a thread pitch of 1.5mm.

Thickness is 7mm, and spanner width is 50mm.

Modeled with ISO profile, using tolerance 6H from ISO 639-3 (minor diameter can be up to +0.3mm).

Therefore, I modeled it with a +0.15mm margin, which should be enough whether you over or under extrude. Note however you still need XY hole compensation in slicer.