sayco stems for shower hot, cold

I replaced yesterday my tub valve stems with a sayco stem kit for bathtub (with knobs & all) from home depot.
my original stems were also sayco and the hot & cold had a small leak so the kit replaces all three (hot, middle diverter and cold)
question I had was about the small nut closest to the handle where I can tighten the stem before I screw it in. how tight should this be? currently with the new stems in, there is a small leak of water from the cold side when I open only the hot side and am not sure if that is due to the middle diverter stem or the cold stem needing the nut to be tighter
I did first handtighten it and then with a small wrench, turn it 3/4 of a turn as I was afraid to overtighten it.

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