d = 4;
r_massive = d/2;
r_nipple = 2.5/2;
distance = 24;
nipple = 3;
$fn = 50;
cylinder(distance, r = r_massive, center = true);
translate([0, 0, distance/2 + nipple/2])
cylinder(nipple, r = r_nipple, center = true);
translate([0, 0, -distance/2 - nipple/2])
cylinder(nipple, r = r_nipple, center = true);