In-hex sockets are a type of socket that fits a six-sided (hence, the name hex for hexagonal), bolt or nut. Hex sockets can either be six or twelve-point sockets. When you have a six-point device, it means that it has six angles that fit inside the end of the bolt, creating a perfect hexagon. Meanwhile, a twelve-point socket is called a bi-hex or a double hex. As the name suggests, it has twelve angles (or points), which you can find in the bolt end.
When you have a double hex, it can fit a hexagonal bolt head two times more than a regular hex socket in terms of positions. Therefore, if you are working in constricted spaces, you may want to choose a double hex socket instead.
For everyday use, however, hex sockets or the six-point sets, are the best option. They are designed to fit the standard nut or bolt head, which are the most common types. These sockets are quite versatile, which is why DIYers and homeowners prefer to work with them.
For your in-hex socket needs, get them here at The Grit.