Final answer:
Fastener threads should always be loaded in tension to utilize their design strength, and never in shear where they are weak and prone to failure.
Step-by-step explanation:
Fastener threads should ALWAYS be loaded in tension or axial load, and NEVER be loaded in shear.
When fasteners are used in mechanical assemblies, they primarily function to hold components together while bearing various types of loads. The threads of a fastener are designed to be strong in tension, where the force is applied along the axis of the fastener. This is because the threaded interface is most efficient and effective when dealing with forces that are pulling it apart or pushing it together along its length.
Conversely, threads are weak in shear, where the force is applied perpendicular to the axis, like trying to slide the fastened parts across each other. Loading fastener threads in shear can lead to premature failure because the threads are not designed to resist sliding forces, and such conditions could cause the threads to strip or the fastener to break.