[ExI] Thermal expansion - Ball and ring experiment

[Emlyn]

I was just in a "heated" discussion with a friend about a twist on the
classic ball and ring experiment:

http://www.physics.usyd.edu.au/super/therm/tpteacher/demos/ballring.html

When the ring is heated, it expands, and so the hole gets larger, and
you can pass the ball through the ring, even though the ball doesn't
fit through the ring when the ring is at room temperature.

The point of contention was this: What if there was a gap in the ring
(so it is now a letter "C" shape). Will the gap in the "C" close or
open further on heating?

My contention is that the gap will get larger, only in that the entire
C shape scales up as it is heated.

My friend's contention is that the gap will become smaller, (because
the metal expands into the gap).

I can't find anything online even close to settling this score. We
tried some experiments with wire rings and the gas stove top playing
the role of bunsen burner (amazingly no one ended up branded for
life), but it was inconclusive.

Any pointers to anything that can settle this argument?

Emlyn