A Hex bolts/Hexagonal Bolts is a form of threaded fastener with an external male thread. Hex bolts/Hexagonal Bolts are very closely related to screws. Hex bolts/Hexagonal Bolts are often used to make a bolted joint. This is a combination of the Hex nut/Hexagonal Nut applying an axial clamping force and also the shank of the Hex bolts/Hexagonal Bolts acting as a dowel, pinning the joint against sideways shear forces. For this reason, many Hex bolts/Hexagonal Bolts have a plain un-threaded shank (called the grip length) as this makes for a better, stronger dowel. The presence of the un-threaded shank has often been given as characteristic of bolts vs. screws,  but this is incidental to its use, rather than defining.