RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Steel Plate Mail Body
The Old School RuneScape Wiki also has an article on Steel Plate Mail Body.

A Steel Plate Mail Body is a plate mail body which can be worn by players with at least level 5 defense. It can be made at level 48 smithing from five steel bars, granting 187.5 experience. It can also be bought from Horvik's Armour Shop.

A steel plate mail body spawns in the centre of the Lava Maze in the Wilderness, next to a Lesser Demon. Some players have chose to use this to make quick cash, either by banking and selling the Steel plate mail body or casting High level alchemy on it.