MM = 1;

CUT_WD = 10*MM;
BORE_DIAM = 6*MM;
SPACER_HT = 7.25*MM;
HEIGHT = SPACER_HT + 3*MM;
THICK = 16*MM;
WIDTH = 18*MM;

BIG = 20*MM;

$fa = 0.1;
$fs = 0.2*MM;


difference() {
  intersection() {
    translate([-WIDTH/2, -THICK/2, 0])
      cube([WIDTH, THICK, HEIGHT]);
    cylinder(h = HEIGHT, r = norm([CUT_WD/2, WIDTH/2]));
    rotate([0, 90, 0])
      translate([0, 0, -BIG/2])
      cylinder(h = BIG, r = norm([HEIGHT, CUT_WD/2]));
  }
  union() {
    translate([-BIG/2, -CUT_WD/2, SPACER_HT])
      cube([BIG, CUT_WD, BIG]);
    translate([0, 0, -BIG/3])
      cylinder(h = BIG, r = BORE_DIAM/2);
  }
}