infty = 100;
eps = 0.01;

diameter = 20;
thick = 2;
d_minus = thick/2; // cca 45 deg

center_hole_d = 3;
side_holes = 5;
side_hole_d = 5;

module body() {
	cylinder(r1 = diameter/2, r2 = diameter/2-d_minus/2, h = thick/2 + eps);
	translate([0, 0, thick/2-eps])
		cylinder(r2 = diameter/2, r1 = diameter/2-d_minus/2, h = thick/2 + eps);
}

difference() {
	body($fn = 128);
	translate([0, 0, -eps])
		cylinder(r = center_hole_d/2, h = thick + 2*eps);
	if (side_holes > 0) 
	for (angle = [0:360/side_holes:360]) rotate([0, 0, angle])
		translate([diameter/4 - d_minus + center_hole_d/2, 0, -eps])
			cylinder(r = side_hole_d/2, h = thick + 2*eps);
}