thickness = 2;
toprad = 15;
bottomrad = 10;
radius = 25;
height = 30;
inside_height = 15;
cube_size = 10;

module holder_round(){
    rotate_extrude(angle=360, $fn=360){
        polygon([
            [toprad, 0],
            [bottomrad, inside_height],
            [bottomrad+thickness, inside_height],
            [toprad+thickness,thickness],
            [radius-thickness,thickness],
            [radius-thickness,height],
            [radius, height],
            [radius,0],
            [toprad,0]]
        );
    }
}

module cube_cut(){
    translate([5,-cube_size/2, thickness]){
        cube([2*cube_size, cube_size, 100]);
    }
}

cube_size = 10;
difference(){
    holder_round();
    for(i=[0:3]){
        rotate(90*i, [0,0,1]){
            cube_cut();
        }
    }
}