Which torque value is required to continue turning a self-locking fastener prior to contact?

The correct answer is the running torque, which refers to the amount of torque needed to keep a self-locking fastener turning after it has been initially engaged but before it reaches its final position. Understanding running torque is crucial when dealing with self-locking fasteners, as these types of fasteners are designed to resist loosening under vibration or movement.

When a self-locking fastener is installed, it typically requires a certain amount of torque to overcome the friction and the locking mechanism to continue turning. The running torque is especially significant because it reflects the force needed to maintain movement without reaching a point of significant resistance or engagement with surfaces that could cause the fastener to become stuck.

In practical applications, knowing the running torque helps prevent excessive force that may damage the fastener or associated components, while also ensuring that the fastener is properly secured. This concept is critical for maintaining integrity and safety in mechanical assemblies.