How can I turn a mesh inside out I have a mesh with bottle threads on the outside.  Now I would like to make / invert the threads so they appear on the inside to create the cap.   I tried using the boolean modifier and difference with another shape but it doesn't create the threads on the inside (it creates the difference of the threads, a gap).  How can I do this with Blender?  I'm also willing to do this mathematically if needed.
What I have.

I would like the threads to look like the image below.

If I scale it by -1 the threads aren't created on the inside. See image below.
Just to illustrate @batFINGER's comment.
You can flip the profile by scaling it by -1.

Select the profile
Set pivot point to one of the vertices through Pivot point &gt; Active element
Scale it along X axis by -1