I’m going to backpedal on this one. It’s true that “slender” is the consensus I’ve heard from most experts, but I’m interested to see what other knowledgeable people have to say. Mike Hagley, who has forgotten more about pipes than most of us will ever know, posted this to a Google group almost 22 years ago:
LB was one of the Quaint shapes that Dunhill introduced years and years ago. Other Quaint shapes were K, EK, US and others so marked with a alpha shape designation, as opposed to a numerical shape designation, such as 40, 59, 60, 120, 127, etc. It is largely believed that LB stood for large billiard, however even Dunhill cannot confirm that (I have letters from them in which they claim they do not know what LB originally stood for, although they suggested that large billiard sounded reasonable).
A certain amount of mystery absolutely remains regarding the origin and explanation behind most Dunhill alpha shape codes, so perhaps the whole Large Billiard thing is plausible guess hardened over time into meretricious certainty. It wouldn’t be the first time I’ve seen that happen.