Quaternary

Quaternary or quatrefoil means four, in this case, it describes a four-cornered Celtic knot design. According to George Bain, a Scottish Celtic art professor, Celtic knots with a closed path are a symbol of eternity or the infinite. Whereas those with open paths signify a journey both physical and spiritual.

These influences are captured in the quaternary symbol to convey the importance of direction and balance. The Quaternary can represent the four Latin Gospels in the Book of Kells, the four cardinal directions: North, South, East, and West, or the four elements of Earth, Fire, Water, and Air. As with most Celtic symbols, there are multiple meanings based on your point of view, time period, or even depending on your mood.

The chain loop is designed to fit a 2mm  diameter chain.  

The Celts viewed the passage of time, especially the seasons with deep seriousness. Let’s face it, the survival of an entire tribe could easily be threatened by a harsh winter or a drought in summer. In this light, the quaternary served as a kind of sigil. The impression of this symbol is thought to be a protective mark, thwarting negative effects in nature.