Hardware a.k.a. nuts and bolts are the parts you need to make your longboard and skateboard complete and connect all the parts. These are the bolt that connects your trucks to your board. Based on the thickness of the boards and if you use/do not use any risers, you can select the right length of the bolts. see also What is the right riser pad?

We have different thicknesses of risers/shock pads and different sizes of Phillips nuts and bolts.