Hex nut
Hex nuts are one of the more popular types of nuts used in the fence industry. They are named for the shape of the nut, which, when viewed from the end, is a hexagon shape with a threaded hole in the middle.
Hex nuts come in a variety of sizes and weights, and they are made in galvanized steel, zinc-coated steel, and stainless steel, and may be painted to match fencing.
One drawback of hex nuts for fencing is that they are easy to remove, with a wrench or shifter, which makes them less secure than some other kinds of nuts that are used for fencing. However, this can be mitigated by applying glue before tightening the nuts, or by tack welding the nuts in place.