Mavic Ksyrium Equip question

What exactly prevents the freehub body from sliding off of the wheel? Is it a locknut? I took everything apart for a good cleaning and can't figure out what happened... driving me N U T S ! The whole thing slides right off, cogs and all. Thanks. DS

Too dumb of a question?

The axle does. It's two pieces that are screwed into each other. When the axle halves are assembled, the freehub is not coming off. That's it. Nothing tricky.