difference()
{
    union()
    {
        cylinder(d = 50,h = 5, $fn = 200);
        cylinder(d = 25,h = 15, $fn = 200);
    }
    union()
    {
        translate([0,0,-5])cylinder(d = 15,h = 50, $fn = 200); 
        for (angulo = [45:45:360])
        {
         rotate([0,0,angulo])translate([20,0,0])cylinder(h = 12, d = 3, $fn = 50, center = true);
        }
    }
}