materialthickness = 3;
diameter = 40;
depth = 10;


union(){
difference(){
    circle(40/2);
    for(rotation = [0: 45: 360]){
    square([materialthickness,diameter], center = true);
    rotate([0,0,rotation])
    {
        square([materialthickness,diameter], center = true);
        }
        }
}
circle((diameter/2) - depth);
}