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

A Mithril Plate Mail Body is a plate mail body which requires at least level 20 defense to wear. It can be made from five mithril bars at level 68 smithing, resulting in 250 smithing experience, or bought from Horvik's Armour Shop in Varrock.

Thrander can change this item into a Mithril Plate Mail top.

It is the third best body armour available in RuneScape Classic, providing less protection than the Adamantite Plate Mail Body but more than the Black Plate Mail Body.