The White hub is just a threaded hub, not a freehub, so the freewheel mechanism has to be part of what you thread on. White make some very nice (and pricey) freewheels:
http://www.whiteind.com/singlespeedgear ... heels.html
but it's a standard thread that's been in use for a hundred years, and any standard (BSC threaded) freewheel will work. Shimano ones aren't bad. Just avoid mini BMX freewheels (usually with 15 teeth or less) and Left-Side-Drive reverse threaded units.
Calmes dans le demi-jour
Que les branches hautes font,
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De ce silence profond.