Indeed they do as my newly completed 4D 3xp7 4x18650 mag would suggest.
Cheers DW :twothumbs, pics soon.
Although its a different ball game to have dual bore, it would have to continue into the tailcap.
4 fit fine i have 20w mr16 running on 4 18650, and you need space in the tailcap for the smaller spring, 4th 18650 stops right before the cap. that are unprotected cells, protected might be longer.
but dual borred only will fit 3 .
4 will stick past the thread. i tried, really no way.