The nut K 27258 secures the fuel pressure valve in the Sulzer ZV40/48 and is a small but safety-critical fastener: it holds the valve body, maintains sealing compression on washers/O-rings, and resists loosening from vibration and pressure pulses. Typically made from high-strength, corrosion-resistant steel and fitted with the specified torque (and locking means where required), correct installation prevents leaks and pressure loss. Include this nut in routine inspections — replace if rounded, corroded or if preload is lost to ensure reliable fuel pressure control.