what are splines? i know they make the cranks and hub stronger, but what are they?

they are ridges on the ends of the axel. if you look at them from the side, they look like a star with many points.

Re: splines

Here are some past threads that explain splines:
Thread 1
Thread 2

And Steve Howard has some good pictures of splined cranks and hubs in his gallery
Steve Howard’s gallery
Specifically this gallery
KH Style 8 Spline Hubs