do they have different cogs than typical flip flop hubs? i bought a 13 tooth cog off of ebay that was off of one n it dosent fit n has two kinds of threads on it.https://cgi.ebay.com/ws/eBayISAPI.dll...MEWN:IT&ih=019

Pista hubs have standard fixed threading on one side only.
Actually, I don't understand exactly what you are asking.

i thought i was geting a cheap 13 tooth cog to mess with but it dosent fit. dang.

This should go for a "most confusing post" batty (to the back of the head).

whats up with that cog. what does it fit. it dosent fit my wheel.

Instead of a Phil/Campy/Miche(?) cog, perhaps you got a Japanese/Surly etc cog. They use different threading (I'm too tired to do your research for you and find out what the exact stats are; check Sheldon (34tpi vs ???).
By all means though, DON'T FORCE IT. Get the right one.

Wait, wait.

If the cog is this one (photo taken from e-bay), then the cog IS NOT for fixed gear and it doesn't come from a Pista Campy Hub (I know bacause I have several old campy track cog, they're all stamped "Campagnolo" with markings of teeth number and threat and they're very different)

I think this cog is from an OLD screw-on cassette (sorry I don't know the exact name in english), the "hole" is much larger than on a fixed gear cog and doesn't fit on a track hub

Looks like the ****tyest cog ever made, and probably not a track cog. The fact that it came "with" a track wheelset doesn't mean it was on the hub. Could well be an ancient freewheel cog by the looks of it.

thanks aldone. i think you are right.

The SHimano name for the hubs where the last sprocket screwed on was uniglide.