Hi andras,

There are a few steps that have to be taken with screw thread type sweeps, without the .3dm file it's hard to say what's happening with your case, but for setting up the helix, make sure that the axis of the helix is pointing in the Z direction and that the sweep option 'Twist' is set to 'Flat' and that the profile is touching the helix or rail curve.

There is a discussion here about the same thing http://moi3d.com/forum/messages.php?webtag=MOI&msg=2133.6

Cheers