My wing bolts are 1/4x20, going into hardened tapped ply. I think they're strong enough. They are retained in the wing with round rubber grommets on the holes on the underside of the wing and a little O-ring of fuel tubing on the shaft site of the 1/4x20 nylon bolt.
What prop are you using with your moki ?
I'm running a 19x8 Mezjlik spinning at 7700-7800RPM. That's about about 23 lbs of static thrust, or about a 1.7:1 thrust to weight ratio. This thrust numbers is calculated (using ThrustHP), not measured.