The clasp is a small component with an outsized effect on security and comfort. Heavier chains generally benefit from clasps designed for greater load and positive engagement.
Lobster clasp
Common, compact and easy to operate on many everyday chains. Quality varies with metal thickness, spring mechanism and size.
Box clasp
Often used on wider chains and bracelets. Better examples may include one or more safety catches, which provide additional retention.
Spring ring
Light and unobtrusive, commonly found on fine chains. It may be harder to operate for people with limited dexterity.
Inspect wear points
Check jump rings, solder joints and the clasp tongue or spring. On valuable chains, periodic inspection by a jeweller is sensible because worn components can fail before the chain itself.