The main RuneScape Wiki has an article on: Nails
The Old School RuneScape Wiki also has an article on Nails.

Nails are an item that can be created by the player at level 34 smithing by using a bar of steel on an anvil whilst there is a hammer in their inventory. Each bar yields 2 nails, and awards 17.5 smithing experience.

12 nails are required to repair the ship purchased from Klarense during the Dragon Slayer quest. This quest is the only known use for nails that there is in all of RuneScape Classic.

Trivia

  • Nails were likely going to be further utilized by players training the Carpentry skill- which was ultimately never finished or released for RuneScape Classic.

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