RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Arrow shafts
The Old School RuneScape Wiki also has an article on Arrow shafts.

Arrow shafts are items used in the fletching skill to create arrows. They can be made at level 1 Fletching by using a regular log with a knife, giving 5 Fletching experience and producing 10 arrow shafts.

Arrow shafts can be made into arrows by attaching feathers to the shaft to make headless arrows, giving the player 1 Fletching experience per headless arrow. The player can then add arrow heads to these, giving an amount of Fletching xp based on the type of arrow head. Arrows can then be used with a bow to inflict damage on opponents in the ranged skill.

Arrow shafts are one of the more commonly traded items among players on RuneScape Classic, and there is a comparatively large demand for them if a player has a large quantity.

Arrow shafts for arrows are one of the most common uses for logs in RuneScape Classic.