Material: special tool steel, hardened and tempered Surface finish: blackened according to DIN 50938. A wrench is an essential tool for a cyclist on the road. How to use the device: To replace a broken spoke on the right side of the rear wheel, first remove the sprocket. The key should be inserted into the cassette nut and then turned with the pedal. The force of 40 Nm transmitted through the chain will loosen the nut, allowing the cassette to be disassembled and the broken spokes to be replaced.