The hand brake cable, also known as the parking brake cable or emergency brake cable, is an essential component in a vehicle's braking system. Its primary purpose is to engage the parking or emergency brake, providing a means to secure the vehicle when parked. Here are the main purposes of the hand brake cable:

1. **Parking Brake Activation:** The primary purpose of the hand brake cable is to activate the parking brake system. When the driver pulls the hand brake lever or engages the parking brake pedal, the cable transmits the force to the rear brake system, causing the parking brake to engage.

2. **Securing the Vehicle when Parked:** The hand brake cable allows the driver to securely park the vehicle on inclines or flat surfaces. Engaging the parking brake helps prevent the vehicle from rolling unintentionally, providing an additional layer of safety in addition to the transmission's park position.

3. **Emergency Braking Function:** In emergency situations, the hand brake can be used as a supplementary braking system. While it is not as effective as the primary foot-operated braking system, engaging the hand brake can provide some additional stopping power in the event of brake system failure or other emergencies.

4. **Compliance with Safety Regulations:** Parking brakes are a legal requirement in many jurisdictions. The hand brake cable ensures that the vehicle complies with safety regulations by providing a means for secure parking.

5. **Preventing Transmission Strain:** Engaging the hand brake when parking also helps reduce strain on the transmission's parking pawl. This can be particularly important when parking on steep inclines, as the hand brake helps distribute the load and prevents excessive stress on the transmission components.

6. **Maintenance of Brake Components:** Regular use of the hand brake helps in maintaining the proper tension in the brake cables and keeps the parking brake system in good working condition. This can contribute to the longevity of the brake components and ensure reliable operation.

7. **Convenience for Manual Transmission Vehicles:** In vehicles with manual transmissions, the hand brake is often used as an additional safety measure when parking. Engaging the hand brake prevents the vehicle from moving even if the transmission is in neutral.

It's important for drivers to use the hand brake regularly, especially when parking on slopes or uneven surfaces, to ensure proper function and longevity of the hand brake cable and related components. Periodic inspection and maintenance of the hand brake system are also recommended to address any issues promptly and ensure the safety of the vehicle.