The goal of this chapter is to give readers a broad overview on the state-of-the-art manufacturing and metrology technologies for spray holes of diesel fuel systems. Spray hole geometry affects the fuel atomization and spray pattern and therefore it is a critical part for enhancing the combustion efciency and reducing the particulate emission. This chapter starts with an introduction of micro-hole electrical discharge machining (micro-hole EDM) and then explains the current method employed to drill spray holes, EDM process monitoring, spray hole measurement, and EDM process control. Finally, it concludes with remarks on future work and the scope beyond. A section of questions and reections is prepared for the interested readers to think deeper and out of the box.