Hi Larry

I vaguely recollect this Tangent lines to two circles from a few years ago.

https://en.wikipedia.org/wiki/Homothetic_center

https://en.wikipedia.org/wiki/Tangent_lines_to_circles

Still researching...

- Brian

There is a MoI tan/tan tan/tan snap, if the start and end points are in the vicinity (by eye) of the tan points..