[Peggy Beryl]

The information page on Ravelry has a link to allow you to see the first page of the pattern. On that page, it specifies sport weight yarn; so you should be able to use any sport weight, usually a #2 weight in the American system, not sure about the Australian equivalent. I shall research now to see if I can find further info.

EDIT: Here is a chart which gives comparative weights for the various geographic areas. You might want to make a copy for future use.

http://www.crochet-knit.com/yarn_conversion.html