Hag Stones, are known by many different names; such as Holey Stones,  Hex Stones, Odin Stones, Ephialtes Stones, Wish Stones, Nightmare Stones and even Witches Riding Stones in some areas.

The hole running through them is naturally formed, by the action of water. They are often found on the sea shore, or discovered in a river or stream bed.

The old belief that harmful magic cannot work on running water may help to explain why these naturally hollowed stones are often seen as so powerful protective. The tunnelling effect of the waters erosion, seems to have imbued it natural with protective powers.

Thus, they were linked with protection from many forms of magic in the past.

Invocation to the Holy-Stone

I have found A holy-stone upon the ground.
O Fate! I thank thee for the happy find,
Also the spirit who upon this road Hath given it to me;
And may it prove to be for my true good
And my good fortune

Leland, Charles. Aradia, Gospel of the Witches

It was thought that naturally formed Hag Stones offered both protection as well as good luck; so they were always highly valued. In the past they were often used by Fairy Doctors and Cunning Folk in charms to counter acts of bewitchment, or when maleficent witchcraft was suspected.

One such traditional charm was to string an odd number of Hag Stones, onto to a length of natural twine or string. Every stone has several knots tied between them. Each of these knots being  tightened as a protective charm is said aloud. Thus binding its power to keep them from harm into every single knot.

This charm was then hung near to the front door of the home (inside or out), as a powerful protection from harm.