$fn=120;

difference() {
	union() {
		cylinder(d=25, h=15, center=true);
		intersection() {
			cylinder(r=25/sqrt(3), h=12, center=true, $fn=6);
			cylinder(r=0.95*25/sqrt(3), h=12, center=true);
		}
	}
	cylinder(d=18, h=20, center=true);
}