Buy OSRS Mahogany plank
The mahogany plank is the highest level plank in Old School RuneScape. Players use it to train the Construction skill and build some of the best furniture in the game. Each plank gives 140 experience when used in a player-owned house. The lowest level needed to build with mahogany planks is 40, for a tip jar or a mahogany bookcase.
Mahogany planks give even more experience in other places. They give an average of 346.1 experience in expert Mahogany Homes contracts, with the completion bonus included. They give 350 experience when fixing broken bridges in the Hallowed Sepulchre. They also give 105 experience when used to build mahogany repair kits.
Making these planks yourself is costly. A sawmill charges 1,500 coins per plank, and the Plank Make spell costs 1,050 coins plus runes for each cast. Buying planks ready to use skips that cost and saves time.
The plank weighs 0.8 kg. It is tradeable and noteable, but it does not stack and cannot be worn. It is also needed in two quests. Cold War needs 1 plank for penguin bongos, and Making Friends with My Arm needs 5 planks for a mahogany coffin.