Helm

From DwarfFortressWiki

A Helm is a piece of Armor covering the head. It can be made from leather, metal, bone and shell. When made from leather it is part of the leather armor set. When made from metal, bone and shell it is part of both the chain and plate armor set.

The Plate Armor Set:
Head: Helm

Upper Body: Plate mail

Lower Body: Greaves

Feet: Boot

Hands: Gauntlets