Buy RS3 Saw
The saw is a basic tool in RuneScape 3. It is used mostly for the Construction skill. Most items you build in your player-owned house need a saw and a hammer. The saw is not used up when you build, so one saw lasts a long time. It is also used during sawmill training.
The saw weighs 1 kg and can be stored on your tool belt, so it does not take up backpack space. It is tradeable and noteable, and free players can use it. Its examine text says it is good for cutting wood. The saw can also be disassembled for parts like cover parts, simple parts, and padded parts.
You can also find a saw in a tool store 1 in a player-owned house workshop, or from a crate during sawmill training. If you want a better version, the crystal saw from The Eyes of Glouphrie quest gives a hidden +3 boost to Construction when a saw is required. For most players, a regular saw is all you need to start training Construction and building your house.