FAQ 46300 COMET II THREAD SIZES
Structure related screws/bolts for Nova Comet lathes are M8x16 or M8x20--most anything that threads into the bed or other casting to attache something will be M8 x something (feet, plastic lock handles, motor lock handle, finger jig bracket).
Stress related nuts/bolts to add bed extension, mount headstock to bed, lockdown tailstock and toolslide--will be M10.
Simple assembly related hex cap screws and grub/set screws will be M6. Screws to attach motor mount plate are countersunk M6x16.
Complex sub assembly mechanisms like the index lock and grinder safety shield attachment will have M4. Most, if not all, take a 3, 4, 6 or 8 allen key.