Hardware
Hardware (or Mounting Hardware) are the nuts and bolts used to mount Trucks onto a skateboard Deck. They come in many different lengths, colors, Screw Head Shapes, and Screw Drive Types.
For most applications, you'll probably be using 1" bolts (with no Risers) or 1-1/4" bolts (for 1/8" or 1/4" Risers).
There are two main screw drive types, Phillips or Hex (Allen) . Phillips screws can be stripped pretty easily if you aren't careful, especially if you don't use the right bit, but hex screws are less prone to this type of damage.
Most bolts have a flat-heads or a truss-heads . The main difference is that flat-head bolts mount flush with the Grip Tape and the rounded truss-head bolts stick up a little bit above the grip tape and can be felt with your feet. For that reason, flat-head bolts are much more common. Truss head bolts were mostly used on old-school setups.