What does the acronym FN refer to in machining?

In the context of machining, the acronym FN refers to "Force fit." This term describes a type of assembly method where two components are joined together with such tight tolerances that significant force is required to assemble or disassemble them. Force fit is crucial in applications where slip or movement between parts must be minimized, ensuring that they function reliably under operational conditions. This method is often used in situations where alignment and stability are key for performance, such as in high-stress components where precise mechanical properties are critical.

The other options presented do not have established meanings within the field of machining. For instance, "Fixed notch" may imply a specific characteristic of a component but does not represent a standard term. "Friction neutral" is not commonly used in machining terminology, and while "Fastener number" could describe a categorization system for fasteners, it does not align with a widely accepted definition in the context of FN. Thus, understanding "Force fit" is essential in comprehending how components interact in precision machining.