What are nuts used for?
Both the bolt and the nut grip the materials being fastened, creating a bolt joint, with the nut also preventing axial movement.
The effect of the bolt joint comes down to the axial clamping force provided by the nut and the shank of the bolt, which acts as a rod that presses the joint against sideways shear forces. This is why so many bolt shanks are threadless – it makes for a stronger rod.
It’s often assumed that the difference between bolts and screws lies in the tools used to install each – a screwdriver for a screw and a wrench for a bolt. This isn’t always the case, however. Bolts can have heads that we associate with screws and require a screwdriver for installation. Even some screws use nuts, so we’re dealing with gray areas.