The nut K 27209 is an unglamorous but safety-critical fastener that secures the fuel injection valve assembly on the Sulzer ZV40/48. By clamping the valve body and keeping sealing surfaces and washers compressed, this nut helps maintain injection pressure and timing while resisting loosening from vibration and pressure pulses. Made from high-strength, corrosion-resistant steel and fitted to a specified torque (often with a locking device), it’s a small part whose correct installation and periodic inspection prevent leaks, misfires and costly engine downtime.