RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Railing (Dwarf Cannon)
The Old School RuneScape Wiki also has an article on Railing (Dwarf Cannon).

A Railing is a quest item from the Dwarf Cannon quest. A bunch of them are given by Dwarf commander in order to player to fix the railings surrounding Coal Trucks and strengthen the defences against goblins in the south.

Repairing the railings is easier with higher Crafting levels. Failing to repair a railing causes 2 or 3 damage.