M6 hose nipple for intake manifold

I am using the "option 4" for pneumatic carb sync (using the M6 hose nipple). I know there are other methods, but I have found disconnecting the resonator tubes is not so easy, and I prefer this option.
I am using Carbtune to measure vacuum pressure. Carbtune comes from a couple of M6 nipples, but I have found it requires more strength that I can do with my bare hands to fit those nipples. I do not want to use a wrench, because Carbtune instructions explicitly advice against that to avoid damaging the screw hole.

I was wondering if there could be some thread difference on the nipples, so I wanted to purchase the ROTAX nipple mentioned in the MML, figure 7.22. But I can not locate a part number for that, either in the MML or the IPC.

Is the part # available somewhere? Any other advice from someone using this method? (from what I have read in the forums, most people remove the compensating tube / resonator hoses).

Thanks!

Carlos