In my TBH's, the worker bee cell size is 5.3 mm.  Both were begun with
sounthern queens and bees from my standard hives.

I have had bee trees (feral hives) close to my house and under
observation for over 8 years.  Not one such hive has ever survived the
winter.  Unless I am able to seal off the dead hive in a bee tree, it is
the first place to be taken over by a Spring swarm some of which (but
not all) come from my own hives.

Burns