M3HoleDiam = 3.4;
M4HoleDiam = 4.4;

module M3Hole(thickness) {
    rotate([0, 90, 0]) cylinder(h = thickness, d = M3HoleDiam);
}

module M4Hole(thickness) {
    rotate([0, 90, 0]) cylinder(h = thickness, d = M4HoleDiam);
}