Pretty new to this stuff so forgive me for my ignorance

so I’m looking into getting a after market steering wheel and boss and seen a few around and looking on eBay and FB found a few good deals but issue is I don’t know what will fit… I have the hex fitment and I looked online and there’s a fair few with said hex fitment BUT I don’t want to dive into it and buy a second hand boss and it be for a DIFFERENT hex size (there’s a mk2 focus one I’ve seen) but I can’t find anywhere what size the hex is nothing on Google nothing I can find in my Haines manual

the none eBay and FB marketplace ones say they fit which is great but I’m broke so I want something cheep of eBay or fb but I have no idea what would fit

if anyone can enlighten me to the exact size hex I have or point me to cheaper options etc much appreciated