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

The Mithril throwing knife is a throwing knife which can be made at level 57 smithing from one mithril bar, producing two throwing knives and granting 50 experience. They can also be found by smashing Strange Barrels.

To wield this particular throwing knife, an attack level of 20 and a ranged level of 15 is needed. You can use weapon poison on it to make it a Poisoned Mithril throwing knife.

At level 98 range, with no other bonuses, the mithril throwing knife hits 17 max.