RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Iron arrow heads
The Old School RuneScape Wiki also has an article on Iron arrow heads.

Iron arrow heads can be obtained from Smithing an iron bar on an anvil at level 20 Smithing. One bar produces 10 arrow heads, and gives 25 Smithing experience. With level 15 Fletching, they can be attached on headless arrows, to gain iron arrows and 25 Fletching experience.