Sharp Pencil". Success was not immediate since the metal shaft—essential for the pencil's long life—was unfamiliar to users. The Ever-Ready Sharp began selling in huge numbers after a company from Tokyo and Osaka made large orders. Later, Tokuji Hayakawa's company got its name from that pencil: Sharp. At nearly the same time in the US, Charles R. Keeran was developing a similar pencil that would be the precursor of most of today's pencils. Keeran's design was ratchet-based, whereas Hayakawa's was screw-based. These two development histories – Hayakawa and Keeran – are often mistakenly combined into one. Keeran patented his lead pencil in 1915 and soon afterwards arranged production. After some improvements, his design was marketed as the "Eversharp" pencil by the Wahl Adding Machine Company; by the early 1920s, Wahl had sold more than 12,000,000 Eversharps. Some of the manufacturers are: Pentel, Pilot, Tombow, Uni-ball and Zebra of Japan; Faber-Castell, Lamy, Rotring and Staedtler of Germany; Koh-i-Noor Hardtmuth of the Czech Republic; Bic of France; Monami of South Korea; PaperMate and Parker of USA; Caran d'Ache of Switzerland and numerous Chinese as well as other Asian and European manufacturers. Mechanism types Mechanical pencils can be divided into two basic types: those that both hold the lead and can actively propel it forward, and those that only hold the lead in position. Screw-based pencils advance the lead by twisting a screw, which moves a slider down the barrel of the pencil. This was the most common type in the earlier part of the twentieth century. Many of these have a locking mechanism one way to allow the lead to be pushed back into the pencil. A clutch pencil (or leadholder) tends to use thicker leads (2.0–5.6 mm) and generally holds only one piece of lead at a time. A typical clutch pencil is activated by pressing the eraser cap on the top, to open the jaws inside the tip and allow the lead to freely drop through from the barrel (or back into it when retracting). Because the lead falls out freely when the jaws are opened, its forward movement cannot be controlled except by external means. This can be easily done by keeping the tip of the pencil a few millimeters above a work surface or the palm of one's hand. Some clutch pencils do have mechanisms which incrementally advance the lead, such as the Alvin Tech-Matic leadholder, but these