I've got a part that I want to screw into another part.

Both parts have the same features (there are 2 revolutions over a 15mm height (pitch 7.5mm) with the start angle at 180 degrees going in a clockwise direction) obviously one swept cut and swept.

The 2 cut outs are also the same shape and dimensions.

When lining the 2 up they don't appear to match.

This is for a 3D printing project i'm currently doing and really need these parts to screw together so if anyone could tell me what's gone wrong i'd really appreciate it!

I've attached the 2 parts and a picture to show that they don't line up.

Thanks!