Useful bolts, such as M8 bolts, act as fasteners in conjunction with nuts. Often confused with screws, bolts usually have unthreaded shanks, except for at the ends, to help with resistance to sideways shear forces. The bolts measure 8 mm across the flats of the bolt heads.
When shopping, make sure to get bolts with the correct thread diameter and length for the items you want to hold together. Grab some M8 bolts and finally complete that project you started.