Jump Ring
A small metal ring joining two parts of a piece. The commonest failure point after the clasp.
Jump rings come open or closed. An open ring is a split circle twisted apart to thread and twisted back; a closed one is soldered shut.
Open rings can work apart under load, which is how charms and pendants get lost without the clasp ever failing.
Soldered rings cost a little more and are the right choice anywhere the piece carries weight.
When you are buying
Look at where a pendant meets its chain. If that ring is open rather than soldered, ask for it to be closed, which any jeweller can do in minutes.
Bail
The loop connecting a pendant to its chain. Its inner width caps what chain the pendant will fit.
Chain
Linked metal forming a flexible necklace or bracelet, sold by length, gauge and link pattern.
Clasp
The fastening that closes a necklace or bracelet. The most common point of failure and the most overlooked part of a purchase.
Pendant
A single ornament hung from a chain or strand, worn as the focal point of a necklace.