Going to have a local machine shop make a shaft hub adapter for a Ryobi.

Is there a standard O.D. dimension for the contact face and washer that are used for 16" to 20" props?

What is the general O.D. dimension on props that size and is it necessary to have full surface contact?

What is the thickness at the hub of props this size?

Do not have anything to measure as yet just waiting for props to arrive. Yep, a newbie!!

Thanks for the assist.
mikenlapaz