Thanks for the reply.

It seems the machines that advertise 2'' capacity are twice as much.  The link is one of several brands of Chinese knock off pipe welders, but they start at 2.48'', while most 2'' plastic is 2.375''.  The linked machine has 8 different size dies for larger pipe; I suppose someone could fab a smaller die, but maybe the smaller pipe does better in a four clamp/thicker two clamp machine; I'm just guessing.