The Boss
The iron-boss shield is a round or a kite shield with the argument moved to the middle. The boss is the dome of Iron that stands proud of the face — eight fingers across, no more, or it stops being a boss and becomes a hammer — and the boss is the whole point: the boss is the part that takes the blow so the hand does not.
A journeyman iron-boss shield is an oak face with the boss set proud, and the setting is the work: the boss is riveted, not glued, because the boss is the part that moves, and the rivets are what let it move and come back. A master iron-boss shield has the boss of forged iron and the maker's mark under the dome. A masterwork iron-boss shield is a story event, and the story remembers it.
In the Hand
The iron-boss shield is the third stance, made iron at the center: brace. The fighter behind it aims the boss at the blow, and the boss takes it, and the hand takes what the boss does not give. The boss is not armor. The boss is the argument, and the argument is short: not you, you are behind me.
"Aim the boss. The boss has already finished the argument." — Rumzuck Umbatsch