The main RuneScape Wiki has an article on: Mithril dart tips
The Old School RuneScape Wiki also has an article on Mithril dart tips.

Mithril dart tips are made from a mithril bar at level 54 Smithing, granting 50 Smithing experience and yielding 7 dart tips. Using feathers with them will make Mithril Throwing Darts, granting 1 Fletching experience per dart.

Smithing dart tips require the completion of the Tourist Trap quest.

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