NC internal grinding is a machining technology that uses numerical control (NC) to finish the inner diameter of parts with high precision. It achieves micron-order dimensional accuracy and excellent surface roughness by bringing a high-speed rotating grinding wheel into contact with the inner diameter of the workpiece. NC control allows for strict management of geometric tolerances such as roundness, cylindricity, and concentricity, and enables high-precision machining of complex internal diameter shapes, including tapers and radii. It can be applied to hard materials such as hardened steel and cemented carbide, and is indispensable for manufacturing products that require high functionality and reliability, such as bearing inner rings, gears, hydraulic components, and precision mold parts. It contributes to improved productivity and stabilized quality through automation.