If it is a dialysis bag used in the preparation of biomolecules to remove salt, small amounts of organic solvents, impurities of biosmall molecules, etc.
Then 6000-8000 generally means that the theoretical molecular weight cut-off is 6000 Dalton to 8000 Dalton
The molecular weight cut-off (MWco) is an interval value It is because of this statistically significant range interval.
That is, molecules less than 6,000 daltons theoretically leak out of that dialysis bag, while molecules higher than 8,000 daltons will certainly stay inside the bag.