Why are chamfered washers used under some bolt heads?

Chamfered washers are used under some bolt heads to provide a better load distribution and to prevent damage to the surface being fastened. The chamfered edge allows the washer to fit snugly against the bolt head and the substrate, ensuring a more stable connection. Additionally, they help to reduce the risk of galling and provide a smoother transition between the bolt and the surface, which can enhance the overall integrity of the assembly.