Andy (@AndyCayp) is correct that the number indicates bowl size.
Lots of information about Dunhill nomenclature on the Net. This is a brief summary.
Dunhill has probably put more marks on their pipes and been more consistent in doing so, over the years, and that's part of their allure to collectors. Dunhill is the most widely collected pipe and there are several reliable experts on the topic, like R.D. Field and the volume of nomenclature marks is dizzying. Some links at the bottom of this post.
Most Dunhills will have:
- Date code
- Finish code (or name)
- Shape number
- Size number
Older pipes may have
Date code indicates the year that the pipe made. Introduced for warranty purposes.
Finish code can be "S" for Shell, "A" for Bruyere, etc., but the name may appear instead.
Size number, 1 for the smallest pipes up to 6 for the largest but there have been series of larger pipes like the ODA, ODB, etc.
Patent numbers appear (generally) on older pipes that were made with a patented process. More common in the first half of he 20th century.
Special series of pipes like the Straight Grain, Collector, etc., may be marked differently.
The famous Dunhill white dot on the top of the stem was introduced around 1915 so that customers knew how to orient the stem. Most companies have followed suit.
I'm conversant with Dunhill nomenclature but no expert. Given the value of these pipes, when buying especially, look them up on the Net. When you sell, if the nomenclature is clearly shown, the collectors will know what they're bidding on. David, (@
droy1958), make sure that you show every bit of the nomenclature clearly (as well as the condition).
Links
Dunhill: Markings
Dunhill: Markings
A Dunhill Pipe Dating ...
Dunhill - Pipedia
Hope that this helps.