Lock ring

A lock ring is the name given by archaeologists to a type of jewellery from Bronze Age Europe.

They are made from gold or bronze and are penannular, providing a slot that is thought to have been used for attaching them as earrings or as hair ornaments. Ireland was a centre of production in the British Isles though rings were made and used across the continent, notably by the Unetice culture of Central Europe.

The technology at the time used a slot in the metal to lock the ring to a jewel. Other features included a decorated face plate and a triangular cross-section. Lock rings have been found in modern-day Ireland, France, and Great Britain. Gold was used for the majority of lock rings that have been found, though other artifacts constructed out of bronze, or clay, gold and bronze composite have been found.

...
Wikipedia