with helicoid which extends 39mm more, inside diameter 48~58mm
when extended greasy helicoid is exposed, not fully recommended
but fairly convenient adapter for me who has many M42 lenses, etc.

The helicoid has larger diameter than usual M42-M42 helicoid, so
it may give better close up shooting due to less internal reflection.
(Also me wish someone made 40~80mm helicoid M42->Z adapter.)