My experience with Osborne is their tools are mediocre, well priced, dull out of the box and they have no customer service.
I'll purchase them only as a last resort but that's just my own opinion.
For finding the proper sizes I'll measure the posts with a caliper and get the corresponding hole punch.
I have a complete set now, have holes punched in a scrap piece of leather and just match the rivet I'm using to the punch that was used to make the hole.