Ink refill is to be used with NSN 7520-01-332-2833, 7520-01-332-3967, 7520-00-935-7135, 7520-00-935-7136, 7520-01-386-1604, 7520-01-386-1618 or any retractable ballpoint pen. Pen ball is medium point with black ink and made of durable tungsten carbide.