What is one function of the fillet on a fastener?

The fillet on a fastener serves an important function in aiding stress distribution. When a fastener is subjected to loads, stress concentrations can occur at sharp corners or edges. The fillet, which is a smooth, rounded transition between the fastener and the connected structure, helps to distribute these stresses more evenly over a larger area. This reduces the likelihood of cracks or failure at the joint, thereby improving the overall durability and reliability of the assembly. The design of the fillet can also help to increase the fatigue life of the fastened joint by minimizing stress risers that would typically be present at a more abrupt joint. This is a critical consideration in aerospace applications, where the integrity of fastened connections is paramount. While other aspects such as appearance, weight reduction, and installation may play roles in fastener design, their primary function is not as essential as the role of the fillet in stress distribution.