I agree to stay with aircraft quality fasteners, but it is really a lot more critical that any OD threaded fastener be aircraft quality. The first thing to fail in a fatigue or simple stress situation will never be the nut. Recognize also that any flexing of a bolt (such as a slipping wood propeller attachment) will quickly induce a lot of fatigue damage at the root of the threads of that bolt.
From my industrial experience, a simple Grade 2 nut will fail a grade 8 bolt.