Electromagnetic ultrasonic thickness probes are increasingly used in shield tunneling to monitor the condition of critical steel components such as cutterheads, shield shells, wear plates, hydraulic cylinders, and screw conveyor casings. Unlike conventional ultrasonic testing, electromagnetic acoustic transducer (EMAT) probes generate and receive ultrasonic waves without a couplant, making them suitable for rough, oily, and hard-to-access surfaces. This non-contact capability improves inspection speed and reduces surface preparation time in demanding tunnel environments. During shield tunneling, accurate thickness data helps operators detect wear, corrosion, and other defects before they threaten equipment safety or excavation progress. The probe can be integrated with automated inspection systems to provide real-time measurements and support predictive maintenance. Key performance factors include lift-off distance, material conductivity, surface condition, and temperature. With proper calibration, electromagnetic ultrasonic thickness probes offer a reliable solution for non-destructive testing of shield tunneling equipment, helping contractors improve safety, reduce downtime, and extend the service life of valuable assets. They are especially useful where conventional probes struggle with couplant contamination or limited access, such as cutterhead wear inspection and steel structure condition monitoring. Routine thickness checks can also support maintenance planning, spare-parts management, and quality control during tunnel construction. In dusty, wet, and vibrating sites, robust probe housing and stable signal processing are essential. Operators should verify calibration on reference blocks and record measurement positions for trend analysis. The method complements other NDT techniques and supports safer, more efficient shield tunneling.