Hi Brent,

I was just in two vintage examples from 1780 to 1820 in up state New York in March this year before going to Texas for a Barn repare. Those two examples and other examples I have been acquaintance with probably average (subjective guess) anywhere from 250 mm (~10") to 400 mm (~16".) I do believe there is some recorded data out there, I will see if I can find it, unless someone can put there hands on it sooner for you...

Regards,

j