Then each of these variables subdivide into other options that can change depending on what kind of application it will be used in. Each changeable detail has a handful (or even more!) different options available. And then we can go through the whole range of sizes again for each of those...phew.
So can you start to see how so many different kinds of combinations potentially exist?
Then there's drills, taps, standoffs, anchors, rivets, nuts, washers, pins, pipes, spacers, "O" rings, turnbuckles...and, well I think you get the idea - there's a lot.
And Freeway Fasteners, at any given time, we'll have stocked - at least - 20 types of bolts, 40 types of nuts, 40 types of screws, 10 types of pins, 5 types of rivets, 30 types of washers & lockwashers (and a partridge in a pear tree.)