I am building a 9A.
Vans says 74" on the A models and 72" on the taildragger.
For the -9A with the (I)O-320: the C2YL-1BF/F7663-4, 72" diameter, 7/16" bolts.
For the -9A with the (I)O-360: either the C2YR-1BFP/F7497-2, 72" diameter, or the C2YR-1BFP/F7497, 74" diameter.
Ref: https://www.vansaircraft.com/order-a-kit/hartzell-propeller-order-form/
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However, on the page linked below from an earlier thread on 180 HP engines on RV-9/9As, Scott M. ("rvbuilder2002") indicated that there are NO structural design reasons that would preclude the installation of a 180 HP engine on RV-9/9As. See Posts #29 & #30.
Except one may be able to exceed Vne straight and level.
I included the 180 HP prop choices because there are more than a few RV-9/9As equipped with 180 HP Lycomings, contrary to what Van's originally intended and not an officially recognized option.