I just got mine today and the attachment fits on my round dryer. It definitely seems to hold tight on there, unlike other diffuser attachments I've tried so here's hoping that the morning dry works out well.

And Auntnett's description of the attachment part is right on.
mostly 3a/i/F
Modified CG since Feb 2008
Rotating a lot!
Blog: http://amy51373.blogspot.com/