The marine Gears made with Case-carburised En36 steel were subjected to grinding damage during manufacturing. The MBN measurements have been made on different Gear teeth using three different methods, namely, High Frequency, Medium Frequency and Low frequency MBN measurements with the optimised measurement device and parameters so that the MBN signal from different depth ranges can be detected and analysed. The MBN measurements on these Gear teeth have shown that the grinding damage near the surface (<10μm depth) can be detected using High frequency MBN, any sub-surface damage (within ~40μm depth) can be detected using Medium frequency MBN and the damage in the deeper layers (> 40μm depth) can be detected using Low frequency MBN measurements. The thermal damage caused by Grinding Burn is also clearly revealed by the shifting of the Low frequency MBN peak to lower magnetic field.