The metalsmith skill is used to make furniture, buckets, bins, blocks, cages, and anvils at a metalsmith's forge. (Despite being under the "furniture" menu of a forge, chains are made by metal crafters, and animal traps are made by trappers).
The labor that corresponds to the metalsmith skill is called blacksmithing. A dwarf whose highest skill is "metalsmith" will have the Blacksmith profession. (Confusingly, Metalsmith is the title given to the whole class of metalworking skills, so a Master Furnace Operator/Weaponsmith may gain a profession of Metalsmith, despite having no metalsmithing skill at all)
- Buildings which are built using material-dependent labors (e.g. a trade depot) may require "any metalsmithing skill," but will only raise Metalsmith and not the other qualifying skill (e.g. weaponsmithing). Bug:4899