Takegawa Colortune is a simple and easy to install method of reading your spark plug for fuel mixture efficiency. Installs into your existing plug hole and reveals a readable external color much the same as removing and reading your spark plug after a plug chop. Great for setting up all carburetors and reads close to real time at various throttle positions. This product is not for continual use and only meant for setup while stationary. Fits all 10mm spark plug holes.