RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Iron throwing knife
The Old School RuneScape Wiki also has an article on Iron throwing knife.

An iron throwing knife is the second-weakest throwing knife in RuneScape Classic, above the bronze throwing knife, but below the steel throwing knife. Two can be forged from one iron bar by players with level 22 smithing, yielding 25 smithing experience. They can also be obtained by smashing Strange Barrels.

There are no skill requirements to wield it. Weapon poison can be used on it to make it into a Poisoned Iron throwing knife.