Also look at what size is most commonly available.
Not sure what a Prima is, but the
Racor 500 series is I believe the most commonly available size. It’s much larger than needed for most sailboat engines, but availability of spares can’t be overstated in importance.
If you know your going where
fuel is sometimes questionable, a dual filter setup may be a good idea, not inexpensive though, and buy at least a case of filters.