// a little cube with x = 30, y = 20, z = 10
x = 30;
y = 20;
z = 10;
offset = 4;


difference()
{
    union()
    {
        cube([x, y, z,], center = true);
        sphere( r = z - offset / 2,$fn = 128);
    }
    
    cube([x - offset, y -offset, z+offset / 4], center = true);

    cube([x + offset, y + offset, z - offset], center = true);
}