RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Steel Plated skirt
The Old School RuneScape Wiki also has an article on Steel Plated skirt.

The Steel Plated skirt is a plated skirt that can be made using 3 steel bars at level 46 Smithing, yielding 112.5 experience. It requires level 5 Defense to equip.

It can be exchanged for Steel Plate Mail Legs from Thrander in southeast Varrock, and can be bought from Ranael's Plateskirt Shop located in southeastern Al Kharid.