Thread example doesn't work with diferent radius

[mantielero]

cadquery-contrib/examples/Thread.py

Line 58 in 3902f2b

core = cq.Workplane("XY",origin=(0,0,-d)).circle(4).circle(3).extrude(height+1.75*d)

If you modify the radius, the core won't be affected.

It should be something like:

core = cq.Workplane("XY",origin=(0,0,-d)).circle(radius).circle(radius-1).extrude(height+1.75*d)