In Robertus Anglicus’ commentary on the Sphere of Sacrobosco, he identifies the orb of an eclipse as 12 degrees; presumably the moiety is 6.
This book and translations of all the major commentaries should be made available in English as soon as possible.
Details on the recovery of the meaning of this symbol can be found in:
Physical Evidence for Ritual Acts, Sorcery and Witchcraft in Christian Britain
This is the symbol used to ward off demons in the darker places of the home and church, which I mentioned recently. Recent experiments suggest it is at least somewhat effective.
A fraternal society of Traditional Astrological Magicians.
Now it has a name.