Contact the company from whom you intend to buy a folding prop, provide them with the necessary specs for your boat, and they will tell you what size you need. They will also tell you whether a two blade or three blade is appropriate for your boat.
A lot of old used ones out there.
I did try one of the online selection calculators, but it recommended a very different prop than I've got & the boat mfg recommended. I'm sure it was a data entry error