At the bottom of the link below the author says (without details)
An alternative method for interpreting Cook's distance that is sometimes used is to relate the measure to the F(p, n–p) distribution and to find the corresponding percentile value. If this percentile is less than about 10 or 20 percent, then the case has little apparent influence on the fitted values. On the other hand, if it is near 50 percent or even higher, then the case has a major influence.
Is n the sample size?
https://onlinecourses.science.psu.edu/stat501/node/340/
An alternative method for interpreting Cook's distance that is sometimes used is to relate the measure to the F(p, n–p) distribution and to find the corresponding percentile value. If this percentile is less than about 10 or 20 percent, then the case has little apparent influence on the fitted values. On the other hand, if it is near 50 percent or even higher, then the case has a major influence.
Is n the sample size?
https://onlinecourses.science.psu.edu/stat501/node/340/