Norman Greenwood wrote:
Does the gauge measure the hackle feather from the pin you bend it
round, in which case it includes the thickness of the hackle stem?

Yes, but that doesn't matter.

A gauge is just an estimating tool to help you pick feathers that are
'right' for your hook. And if it looks too small or too big on the final
product, use a bigger or smaller feather for the next one.
--
Stan Gula
http://gula.org/roffswaps