Hello Hepsibar
Well, Webb has a long heritage and I have been
trying to understand the AUS perspective for some years.

The Wasp was the six-bladed 12" model.
It formed a part of the holy Webb trinity:
the Whippet, Wasp, and Witch.

I would rate the Whippet good; Wasp better; and Witch great laugh
[Apologies to Devo fans].

My best guess is that the Wasp was a post-war model
introduced here in about 1947.

I would date AUS sold machines from that time to about the mid-1950s
[based on newsprint advertisements]

It sold over many decades: -
https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/60888/webb-range-1970s.html

An image of your machine may help dating ...

Hope this helps.
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Jack

Attachments
2012_10_ebay_1964_webb_01.jpg (48.46 KB, 46 downloads)
1948_06_smh_09june_p8.jpg (161.29 KB, 46 downloads)
1947_05_argus_29may_p4.jpg (99.61 KB, 46 downloads)