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

The Adamantite Chain Mail Body is the second best chain mail body players can acquire. 30 Defense is required to equip it. It can be made at 81 Smithing with three adamant bars, granting 187.5 experience. It can also be purchased at Wayne's Chains in south Falador.