The Konnyaku Stone is a small but important tool used in the Toyota Production System, where it is used to smooth body panels before they are painted and to eradicate tiny imperfections.
Known as the ‘devil’s tongue’ and the size of a fist, the Konnyaku stone isn’t actually a stone at all – in fact, it’s made of a mix of fine gritty resins.
When the stone is brushed across the metal surface, any small raised imperfections or dust marks will be knocked off or smoothed out. The importance of a completely smooth panel is incredibly important, particularly further down the production line such as in the paint shop.
Before each panel can be taken into the weld shop (the next stage in the production process), a Toyota member has to sign it.
Find out more about the Toyota Production System in our glossary.