Cupping varies from 1-6, where 1 is very "slippery" and 6 has very good grip.
The recommended sizes are preselected for your convenience. If the propeller is to be used for UIM racing then preselected variant can be good average choice.
EU clients buying for a company with VAT ID please order by contacting erik.aaslav.kaasik@hotmail.com to have VAT deducted.