This is our jar. Im trying to replicate those threads exactly. I did a screw modifier as a separate object.
You should create the thread within the same mesh as the rest, but if we keep it as a separate mesh:
- Put your 3D cursor at the center of this object. Set the 3D cursor as the Pivot Point. Select a part of the mesh.
- Duplicate the selection with a ShiftD then Enter. Make the duplication rotate around the Z axis and with the 3D cursor as center.
- Delete the former thread extremity.
- Join the parts with W > LoopTools > Bridge.
- You've got your shape.