Foundation sleeves from 1-3/8 in. to 3 in. are form fitting, meaning pole slip into the sleeve snugly, no need to fill with sand.
Sleeves 3 in. to 3-1/2 in. butt, the opening is 4-1/4, use wood wedges to level pole is the sleeve and add sand around pole for proper installation.
For stable installation 1 ft. of the flagpole should be encased in the ground sleeve below grade for every 10 ft. of exposed flagpole height.