X20128501 is a reset button seal accessory designed for E-T-A thermal overcurrent circuit breaker model 1658 series. This component is specifically engineered for 3/8" diameter openings with 27-thread UNS-2B specifications, providing a secure sealing interface for the reset button mechanism. The seal is manufactured to metric design standards with millimeter dimensions taking precedence over inch measurements, ensuring precise fit and reliable operation. This accessory is essential for maintaining proper circuit breaker functionality and environmental protection in industrial and electrical applications where thermal overcurrent protection is required.