A radiator bleeding tool generally refers to a bleed key that is used to open the air vent plug of a radiator to release any air trapped inside. A radiator with a significant amount of air trapped inside it generally sees a reduction in efficiency.
As of 2015, a radiator bleed key can be constructed from a wide range of alloys and metals, such as copper, aluminium and zinc-plated steel. The material chosen for a bleed key typically does not rust. Radiator bleed keys are also generally found in three distinct shapes, which are the clock key shape, the 'T' design and a bleed key fitted with a long wire handle.