Maudslay’s work on the screw thread was not confined to the lathe. He improved the system of taps and dies whereby they were made to _cut_ the threads instead of _squeezing_ them up, and he introduced the use of three or more cutting edges.[41] He made the first move toward the systematizing of thread sizes and made a series of taps from 6 inches in diameter, for tapping steam pistons, down to the smallest sizes used in watch work. The diameters of these taps varied by eighths and sixteenths of an inch, and their threads were determined by the respective strengths of each screw. He established for his own use definite standard pitches. Many copies of these threads found their way to other shops and influenced the construction of similar tools elsewhere. In fact, Holtzapffel says: “I believe it may be fairly advanced, that during the period from 1800 to 1810, Mr. Maudslay effected nearly the entire change from the old, imperfect, accidental practice of screw making to the modern, exact, systematic mode now generally followed by engineers; and he pursued the subject of the screw with more or less ardour, and at an enormous expense, until his death.”[42] [41] Holtzapffel, Vol. II, p. 646. [42] _Ibid._, Vol. II, p. 647. [Illustration: FIGURE 15. MAUDSLAY’S SCREW-CUTTING LATHE ABOUT 1797] [Illustration: FIGURE 16. MAUDSLAY’S SCREW-CUTTING LATHE ABOUT 1800] While we would not detract from the ingenuity of others who conceived the idea of the slide-rest and lead screw, enough has been given to show that no other mechanic of his day appreciated their possibilities as he did, and none embodied them in forms as useful. The fact that for many years the slide-rest was popularly known as “Maudslay’s go-cart” indicates that his contemporaries recognized him as its originator. The business at Lambeth grew steadily until it employed several hundred men, and embraced the making of saw- and flour-mills, mint machinery and steam engines of all kinds. With his keen mechanical intuition he saw that the cumbersome wooden walking beam characteristic of the Newcomen and Watt engines was unnecessary. He therefore dispensed with it and drove direct from the engine crosshead to the crank, thus making the first direct-acting engine, which held the market for a long time. He built the first marine engines in England, and his leadership in that field was unchallenged for many years. Another of his inventions was the punching machine for punching boiler plates and iron work. His influence was felt in many directions in the field of machine design. He was the first to point out the weakness of the clean, sharp corners in castings which were so prized at that time, and advocated the use of fillets, showing that they greatly increased the strength.