NOCTI Maintenance Practice Test

Preload is the clamping force that a tightened fastener applies to the parts being joined. When you tighten, the bolt elongates and pulls the parts together, creating a compressive force across the joint that keeps surfaces in contact and resists loosening under load or vibration. Torque is the turning effort used to reach that tension, but preload is the actual clamp force produced in the joint. Friction at the threads and under the bolt head affects how much preload you get for a given torque. A fastener’s load rating describes how much load it can safely carry, and shear force is a different type of load acting parallel to the joint. So preload is best described as the clamping force in the joint.