Not all 901 connectors are machined properly to work with cartos; may screw on fine but not have the correct holes or slotting. (In which case the modder or yourself may still be able to adapt it, but not the simplest way to go.) Many mods give a choice of connector style; getting a 510 type and then a 510 to kr808/carto adapter (e.g. from Altsmoke or Good Prophets) is a popular choice, and is what I use and like on two mods. I did also try a 901 to carto adapter on a 901 style
mod and didn't like it at all -- it could achieve either nothing but air or a blue-in-face hard draw, no in between.