**Electrolyte used for fine hole drilling by electrochemical machining is NaCl**

Electrochemical machining (ECM) is a non-traditional machining process used to shape and drill holes in conductive materials using the principle of electrochemical dissolution. In ECM, a workpiece (anode) and a tool (cathode) are submerged in an electrolyte solution, and an electric current is passed through them to remove material from the workpiece.

The choice of electrolyte is crucial in ECM as it directly affects the machining rate, surface finish, and overall performance of the process. Different electrolytes are used depending on the requirements of the specific machining operation. In the case of fine hole drilling, NaCl (sodium chloride) is commonly used as the electrolyte. Here's why:

1. **High electrical conductivity**: Sodium chloride is a highly conductive electrolyte, making it suitable for electrochemical machining. The high conductivity ensures efficient transfer of current between the workpiece and the tool, enabling effective material removal.

2. **Stability**: NaCl is a stable compound that remains in solution and does not break down easily during the ECM process. This stability ensures consistent performance and prolongs the life of the electrolyte, reducing the need for frequent replacements.

3. **Chemical reactivity**: Sodium chloride is chemically inert and does not react with most metals commonly machined using ECM, such as stainless steel, aluminum, or titanium. This inertness prevents unwanted reactions or contamination of the workpiece, ensuring accurate and precise drilling of fine holes.

4. **Safety**: NaCl is a relatively safe electrolyte to handle compared to other options. It is not highly corrosive or toxic, making it easier to handle and dispose of after use. Safety considerations are important in industrial processes to protect workers and the environment.

Overall, NaCl is a suitable electrolyte for fine hole drilling by electrochemical machining due to its high electrical conductivity, stability, chemical inertness, and safety. However, it is important to note that the choice of electrolyte may vary depending on the specific requirements of the machining operation, such as the material being machined and desired surface finish.