Screw on freewheel on a fixed hub thread?

How does it all work, can I literally just slip a freewheel on the thread and tighten it up, I know there are some freewheels that then you pedal they tighten, would this work?[URL="http://www.alansbmx.com/product_info.php?cPath=32_73&products_id=3061"][/URL]

****all ****freewheels will tighten every time you pedal, because it's a freewheel, it doesn't come loose when you stop pedalling unlike a fixed cog without a lockring.

the bike shop who told you this are merely looking out for themselves and never though about putting a freewheel cog on a fixed thread, so they don't know the consquence (at least that what I gather).

but it's perfectly fine, the contact area on the thread will be slighty smaller but plenty enough to run a freewheel cog.