From Longman Dictionary of Contemporary Englishclapperclap‧per /ˈklæpə $ -ər/ noun [countable] 1 APMthe metal part inside a bell that hits it to make it ring2 → run/go/drive etc like the clappers
Examples from the Corpus
clapper• It was a perfect Great Hall of the People crowd: prominent, well behaved; all clappers, no complainers.• He was carrying his hand bell by its clapper, and he shifted his grip to the handle and began clanging.• Little legs going like the clappers.• But apparently these fish do have one redeeming feature - they grow like the clappers.• All their backs were coming up like the clappers.• Sir David is, rather gallantly, hanging on the clapper. 