Usage patterns
留め金を外すto undo/release the clasp
I undid the clasp on the bag and took out the contents.
留め金をかけるto fasten the clasp
I fastened the clasp on the door so no one could get in.
留め金が壊れるthe clasp breaks
The clasp on the necklace broke.
留め金がゆるむthe clasp becomes loose
The clasp on my watch had become loose, so I got it fixed.