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

A steel throwing knife is the third-weakest throwing knife in RuneScape Classic. Two can be forged from one steel bar by players with level 37 smithing, yielding 37.5 smithing experience. They can also be obtained by smashing Strange Barrels.

These require 5 Attack and 5 Ranged to wield. Weapon poison can be used on it to make it into a Poisoned Steel throwing knife.