A mace and chain.
The Mace and Chain is a deadly weapon used by one of Tennyson's henchmen in the Kings of Clonmel. Not to be confused with a mace.
This weapon is uncommon, but poses a large threat to inexperienced enemies. The chain allows the head of the flail to bend around an opponent's shield, rendering it virtually useless. Horace discovers this in book eight when he faces the weapons in a duel against Tennyson's henchmen.