When I used to ask about group size from this one veteran retailer, he would say "It's Dunhill X," and as he said the word "Dunhill," his voice would have an odd inflection. He never said what he was communicating with the inflection, nor did what he say ever make the definition for group size clear. But hey, I'm no dummy, I understood it to be a large pipe, which in my mind approximated a group 6.
But I've been looking at listings for ODAs online and smokingpipes listings at length, in the course of which I found the words behind the acronym, "Over Sized Dunhill." But even in sp writeups, size is by no means the determining factor in the designation. Apparently shape and what Dunhill meant for the size in that shape figure in.
When I want to know size I want to know size, and just size. What does size have to do with shape? Very little, to my mind! The further convolution of what Dunhill meant for size in a particular shape is only of interest for a Dunhill historian. For me these added considerations have amounted only to years of confusion.
I daresay that even among seasoned retailers there is a good amount of confusion. If someone calls about the size of a particular pipe, are they going to say that it's
Dunhill Bruyere (ODA) (850 F/T) (1966/69)
when its chamber is 17mm X 37mm? The caller is going to hear group 6 when the pipe is a 4. Does the retailer really have the time to explain this contradiction? He likely is going to translate what he says into the common use of group sizes.
Even worse, consider:
Dunhill Root Briar Patent (ODA) (834) (1952)
with a chamber of 22 X 29 mm, I would say a prince. So yes the chamber width is oversized for a prince, but the pipe size overall is hardly worthy of of the ODA pronouncement.
Finally there are several indeed large pipes in these listings that are also called ODA.
What a mess!