I've always preferred thinking in terms of the numerical constriction, rather than an arbitrary name whose specific definition is not always the same everywhere.
Properly, choke designations are indicators of pattern performance (percentage of pellet strikes in a 30 inch circle at 40 yards), not a specific constriction. Even using that standard there is considerable variation in how specific loads perform in a given choke designation in any barrel.
I have always spec'ed choke work by supplying ammunition of my choice and specifying pattern percentage to be achieved. This requires care and testing by the 'smith doing the work. Much easier, of course, to specify constriction, which relieves the 'smith of the tedium of cutting, checking, cutting, checking, etc. He need only produce the constriction desired and he's done.
Hard to find a 'smith these days who will bore a gun to the pattern specs provided, rather than just cut to a given constriction.
