Basically, you can combine the FD-NEX adapter and the FD-M42 adapter and use M42 lenses on the NEX without having to buy a dedicated M42-NEX adapter. Admittedly, an M42-NEX adapter is not that expensive, but why not make use of what you have? Even though I don't like multiple adapters, but this combination actually works really well, because breech lock mounts are secured and when mounted, will not have any play at all. Since my FD-NEX adapter has a very good and tight fit, this combo makes a very nice and solid fit.
Old FD-M42 adapters from eons ago.
FD-NEX & FD to M42 mounts.
Both adapters combined and mounted on the NEX-5.
Sample Photo with both adapters -- NEX-5 & Takumar SMC 85mm f1.8