I have an asp 21a ... It was little hard to crank and I tried to loosen it up and ended removing the drive hub... The problem is how do I fix it back I tried to put it back and its so loose that its not attached to the crank .... Can any one help me please?

@rajji,
Should be having a split taper collet (part no 15218 in attached pic)
Once you mount a prop and tighten, it should hold.

Hope this helps.
(Check why it is hard to crank. Don't force anything. If it is gummed up with old oil, give it a shot of WD40. Or soak in methanol)

Well actually its a new engine .... Not broken in yet and thank you very much

Pics of the drive hub and cone

That taper sleeve is split for a reason. It will go in the hub as a light press fit.

Better figure out why it is hard to move. Take out the glow plug and try to turn the engine over. This should happen easily. If not, dissemble the back and check for fouling