This paper refers to a developed measurement process able to interact with small plastic parts, with holes about 0.4mm of diameter with a critical function on the vehicle. This method must be similar to the real condition. In other words, it must represent the fuel passing through these parts, though in a clean and faster way. To do this characterization, a light beam was used, in intensity strong enough to pass from side to side of the cavity up to the hole. This way enabling us to measure the light intensity that goes out. The resultant spread light beam is recorded by a digital microscope and converted in a chart by an algorithm. Based on a model developed, that picture is converted or translated in a number which can be used to separate part types, according to correlation of the spray performances. The main purpose of this methodology is a simple and effective way to monitor the produced parts and ensure the proper operation of the component when assembled in the complete system.