A spindle nut is a type of fastening nut used to secure a wheel hub or spindle to the axle of a vehicle. It is commonly found in automotive applications, particularly in the assembly of front and rear wheel hubs. The spindle nut is designed to provide a secure and tight fit, ensuring that the wheel hub or spindle remains firmly attached to the axle, thus maintaining the integrity and safety of the vehicle's wheel assembly. The spindle nut is typically tightened to a specific torque specification to ensure proper installation and performance.