phxrock, prepare for some frustration on this subject. What you are referring to are Group 1, 2, 3, 4, 5 and 6, which denote
graduated sizes of pipes in a system developed by the Dunhill company. Your best sense of what this means may be gained
from visiting the Iwan Ries online retail site which classifies all of their pipes under this system. You can look up pipes you
may own that they are selling and find out what Groups they are in. Now here comes the frustration. Dunhill doesn't disclose, and
it may be that there are no, exact specifications for these Groups. The generalities are simple enough. Group 1, 2, and 3,
are small pipes for short smokes, sampling, extra strong blends. Group 4 is your standard middle size bowl. Group 5 and
6 are extra large bowls. This system drives engineers and technicians crazy, with no set specifications. For the rest of us, it
gives a general idea, which is all we want or expect.