What qualifies soldiers to receive a clasp?

[wimsey]

The clasps are Sebastopol,Inkerman,Balaklava and Alma. There is also a twin medal broach with a very dilapidated ribbon, yellow with green edging. No actual medal although the swivel mount remains. Probably either sold or lost.
Apil

oh I see (I think). So the clasps don't necessarily belong with your gg's medal ? (or might or might not ?)