The boss of a shield is called a buckle from the Middle English bocle and the Old French bocle or bucle The boss of the shield is the ring of the shield Source Webster s New Twentieth Century Dictionary of the English Language 1943 The boss of the shield in Late Latin is called a bucula or buccula or the beaver of a helmet from the bulging shape Source An Anglo Saxon Dictionary by T Northcote Toller 1921 cited lexicon ff cuni cz html oe bosworthtoller d0110 html