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The older Simpson measurements are from the Somerset outfit bought out by Vulfix and moved to the Isle of Man. Great brushes too but not quite the same as the Somerset measurements AFAIK. At least...

If you go to the Simpson site they specify the loft and knot diameters. I have a chubby 3 and a polo 8 & 10. If you're a face latherer with hard soaps the chubby would be my pick.

I am very fond of the Polo handle. I have big hands though so that might be something to consider. Can't go wrong either way though.