translate(v=[0, 0, 55/2])
difference() {
	cube(size=[20, 20, 55], center=true);
	
	translate(v=[10, 0, 0])
	scale(v=[10/55, 1, 1])
	rotate(a=[90, 0, 0])
	cylinder(h=50, d=55, center=true);
	
	translate(v=[-10, 0, 0])
	scale(v=[10/55, 1, 1])
	rotate(a=[90, 0, 0])
	cylinder(h=50, d=55, center=true);
	
	translate(v=[0, 10, 0])
	scale(v=[1, 10/55, 1])
	rotate(a=[0, 90, 0])
	cylinder(h=50, d=55, center=true);
	
	translate(v=[0, -10, 0])
	scale(v=[1, 10/55, 1])
	rotate(a=[0, 90, 0])
	cylinder(h=50, d=55, center=true);
}