Use this lead with the Zebra DelGuard or any other 0.5 mm HB mechanical pencil. Vigorous quality assurance testing guarantees durable performance for all Zebra products. The lead core is hard enough to prevent the break, which reduces the trouble of replacing the core frequently. The ink is delicate and smooth. Also, the concentration of fine graphite is sufficient. There are 40 leads for each tube. It is stored in a durable and resealable plastic tube for convenience and portability.