Just didn't want to error in making the diameter too small! May have just searched in wrong places and the pics scale objects, they all look about the same.
FWIW:1)
Our 18" is 1-5/8" and our 20" is 1-3/4". Hope that helps.
Thanks Mike Clemmens MSC Propshttp://www.mscprops.com
2) Also measured a DA50 hub yesterday 1.625"
Eiit added:
3) From Windsor Props:
For the 20" props the measurement is 1.75" and 1.80"/
Sincerely,
Fred Jamieson
Windsor PRopeller Company