$fn = 500;

difference() {
    cylinder(h=5, d=14);
    
    translate([0, 0, -0.1]) {
        cylinder(h=6, d=8.4);
        
        for (a=[0:45:360]) {
            echo(a);
            rotate([0, 0, a])
            cube([6, 1, 6]);
        }
    }
}