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The FD 150 will happily bore out the Sherline chucks but there are two problems. 1) How will you hold the chucks to bore them? 2) How will you cut the thread? I bored mine out at 1000rpm taking shallow cuts, no problem with the Proxxon if you can hold them, possibly reversed onto a sleeve on the nose thread.
I then started the thread by screw cutting with a single point tool (not possible on the Proxxon) and then finished with M16x1 taps to get the correct profile. You could tap the thread directly but it will be difficult to keep it square and will require a high torque.
I think the choice of M16x1 is due to the ER11 collets. The standard collet nut for ER11 appears to be M14x0.75 so I could see people trying to fit this onto a M14x1 nose and damaging both.
A step down adaptor will move the chuck further from the headstock bearings so not a good solution.