Mithril Casing is a craftable item in World of Warcraft Classic with various uses. From crafting gear to using it as a quest objective, Mithril Casings are a sought-after item in WoW Classic, especially in its later stages.
How to get Mithril Casing in WoW Classic
Mithril Casing is specifically needed for the quest “Chasing A-Me 01” in Un’Goro Crater. The quest requires you to repair a mechanical gorilla deep in one of Un’Goro’s caves, but you can’t until you’ve found a Mithril Casing.

Fortunately, Mithril Casing is easy to come by since you can purchase it off the Auction House, usually for less than one gold.
Engineers can also craft Mithril Casings. If you are an Engineer, all you need is three Mithril Bars, a Blacksmith Hammer, and an Arclight Spanner to create one Mithril Casing. You’ll also need a minimum of 215 Engineering skill to learn the Mithril Casings recipe.
How to complete A-Me 01 quest in WoW Classic

Once you’ve either crafted or purchased a Mithril Casing, you can return to A-Me 01 in Un’Goro Crater and begin the next (and final) portion of the gorilla’s quest chain. This involves escorting her back to Karna Remtravel just outside Marshal’s Refuge.
Other uses for Mithril Casing in WoW Classic
If you’re not looking to complete the quest “Chasing A-Me 01,” you can also use Mithril Casings as crafting reagents in mid-level items such as the Deepdive Helmet and Thorium Rifle.
Besides allowing you to breathe under water, which can come in handy in Classic, the Deepdive Helmet looks awesome. If only Classic had transmog, eh? Thorium Rifle, meanwhile, is a solid gun with +17 Ranged Attack Power, making it a decent option for Hunters.