minkowski(convexity = 0) {
	difference() {
		square(size = [20, 20], center = true);
		square(size = [10, 10], center = true);
	}
	circle($fn = 16, $fa = 12, $fs = 2, r = 1);
}
multmatrix([[1, 0, 0, 25], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]]) {
	minkowski(convexity = 0) {
		circle($fn = 16, $fa = 12, $fs = 2, r = 1);
		difference() {
			square(size = [20, 20], center = true);
			square(size = [10, 10], center = true);
		}
	}
}
multmatrix([[1, 0, 0, 0], [0, 1, 0, 25], [0, 0, 1, 0], [0, 0, 0, 1]]) {
	minkowski(convexity = 0) {
		union() {
			difference() {
				square(size = [20, 20], center = true);
				square(size = [10, 10], center = true);
			}
			square(size = [2, 2], center = true);
		}
		circle($fn = 16, $fa = 12, $fs = 2, r = 1);
	}
}
multmatrix([[1, 0, 0, 25], [0, 1, 0, 25], [0, 0, 1, 0], [0, 0, 0, 1]]) {
	minkowski(convexity = 0) {
		difference() {
			square(size = [18, 18], center = true);
			square(size = [12, 12], center = true);
		}
		difference() {
			circle($fn = 16, $fa = 12, $fs = 2, r = 2);
			circle($fn = 16, $fa = 12, $fs = 2, r = 1);
		}
	}
}
