Square nuts are typically used in conjunction with square bolts or are commonly used with pole line hardware
Square nuts are four sided nuts as opposed to the more common hex (six-sided) nuts. The surface area on the flats is larger than hex nuts, which reduces wrench slippage. However, you cannot use hex drivers such as sockets and nut drivers. Regular square nuts have a flat bottom bearing surface and a crowned washer-faced top. Regular square nuts are often used with square bolts.