Rivnut / nutsert
Possibly one of the most overlooked pieces of fence hardware is the rivnut, also known as a threaded insert nut or simply a nutsert.
These little pieces of fence hardware install like a rivet, so they're easy to install in a predrilled hole on a post, gate or nearly any other fence component you can think of, but they also have a threaded center, so you can use a bolt to attach cover strips, panels, brackets or anything else you need to to the surface of the fence component.
Some of the common uses for rivnuts or nutserts in fencing are to attach fence panels to gates with custom clips, or to attach extension brackets to posts, but the options really are endless.
Rivnuts are made from a variety of materials, and are available in an array of sizes and diameters, so there's one that's suitable for nearly every application.
Rivnuts or nutserts can be installed using various tools, including larger rivet guns.