module m3Nut(h = 2.4, clearance = 0, center=false) {
  $fn=6;
  cylinder(d=6.35 + 2*clearance, h=h, center=center);
}

module m4Nut(h = 3.2, clearance = 0, center=false) {
  $fn=6;
  cylinder(d=8.08 + 2*clearance, h=h, center=center);
}