10.5 x 3 is as close as I can figure. I used my heli pitch guage and the 10x3 is at the base of the blade. the tips are 0 pitch, just flat. These are odd in a number of ways. They truly just dangl there. They open by centrifical force and the blades can pivit forward to the point that the tips are 7 inches apart and rearward to 2 inches apart. One thing I have done is adapt a very light spring to the blade so they will close when there is no centrifical force at work. I did this because I came in to land on a particularly hot but calm day and the blade was dangleing losely directly down, as the minimoa stalled and dropped from about 1 foot it sort of floated rearward dropping the gliders weight on the one blade and broke it at the point the M2 bolt goes through the hub and prop. That cost me 3 weeks of no flying as I waited for the new prop from Hong Kong. They had 6 in stock, I bought 3. Ask anything else you need. I am retired and around most of the time. I am glad to be of any help to anyone. If I don't know the answer I will lie!! LOL :D
Rather than complicating things with springs et al, if a prop doesn't fold from onrushing air the shoulder screw is likely too tight. Sometimes mold flashing or other burring can interfere, in which case remove blade(s) and sand smooth with fine ~200 grit. I always lubricate my folders with dry graphite powder, rubbing into the micro grooves left from sanding. On reassembly blades should fall under their own weight, and pendulum a couple of swings. Tighten the screws gradually until they stop this slight swinging, then back off very slightly so they will* done. ==== One final comment about "If I don't know the answer I will lie". That's one of the major problems in this world - people who don't know but would rather pretend they do. There's nothing wrong with admitting "I don't know" or even saying nothing. Especially when harm can come to others from guesswork being passed off as knowledge. I realize you might have been joking, but this is no joking matter.
If this is the Art-Tech 2-meter Minimoa - which it has every indication as being - the prop measures 9.45inches (240mm) but is specified (by mfr) as a 9x5. If you're looking for a suitable upgrade prop, the stock prop from the ASW28 glider sold by HK has been recommended but I don't know it's size & pitch.
Note that on the earliest models of Art-Tech Minimoa they were supplying 11x5's which far overloaded the 20A ESC. Rather than just try a higher-amp ESC, which the motor is no powerhouse so can't take the heat, the best treatment was to cut the 11x5 down to 9x5, in effect an inch off each blade. This, according to reports, dropped current draw to about 15A, and retained good "better than scale" climbing ability. Art-Tech soon began supplying the plane with the present 240mm size.
Finally, one recommended replacement is for 9x5 carbon blades, for their gain of efficiency (ie, stiffer). I personally don't think the small gain in performance is worth the cost - but it's your money so your call. If you find this info helpful, would appreciate a credit. Clear Skies!