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

Rune dart tips are made from a rune bar at level 89 Smithing, granting 75 Smithing experience and yielding 7 dart tips. Using feathers with them will make Rune Throwing Darts, granting 1 Fletching experience per dart.

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