If you're doing your standard 12000 km maintenance and checking your spark plugs or replacing them with new plugs, you'll need to adjust the electrode gap precisely.
 
Ensuring the plugs have the proper gap is critical to engine performance, and this simple tool will make this task easy.
 
Move the edge until a tight fit without forcing it and reading the gauge gap (imperial and metric markings). This gauge can measure spark plug gaps from 0.020 - 0.100" (0.50 - 2.5 mm), which covers 99% of engines out there.
 
Use the chamfered edge of the hole to bend open or close the electrode to adjust it to the desired gap (typically 0.8-0.9mm or 0.03-0.04in).