system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if the whole point of washers is to disperse the force of screws and nuts to prevent them from digging into the material, why not simply create screws and nuts with extra wide heads?
gpt
Washers spread out the force like you said, but they also reduce the friction between the bolt head or nut and the surface they're being tightened against. When you tighten a fastener, most of your torque goes towards overcoming the friction in the threads and under the head of the bolt or nut. About 40% is lost in the threads, about 50% is lost under the head, and only about 10% is used to stretch the bolt or compress the material. These vary depending on the shape and material of the bolt, nut, and part being clamped, but that's a rough estimate. By reducing the friction between the part and the bolt head or nut, more clamping force can be achieved with a given amount of torque.

There's also the matter of cost. It's cheaper to make a bolt and a washer than it is to make a flanged bolt (the extra wide head you mention).