The grade-8 aircraft screws and nuts are correct, but early Panteras and Mangustas used virtually identical grade 5 metric screws & nuts; I forget what size they are. Even gr-5 screws rarely break; more often, they're lost or aren't tight enough. As mentioned, the critical point is grip length- no threads in the load areas. And contrary to some, the inboard screws can be installed with the heads facing the ZF so the nuts can be easily torqued. You just have to play with the axle position to find the spot where they can be finagled in place.
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