In boilers as commercially made and sold the difference in quality of the plates and rivets, together with the great uncertainty as to the exact effect of punching the plates, have, so far, prevented anything like the determination either by calculation or experiment of what might be accepted as the best proportions of riveted joints. In regard to steel plates for boilers Mr. F.W. Webb, of Crewe, England, chief engineer of the London and Northwestern Railway, has made over 10,000 tests of steel plates, but had only two plates fail in actual work; these failures he thought were attributable solely to the want of care on the part of the men who worked the plates up. All their rivet holes for boilers were punched in a Jacquard machine, the plates then annealed, and afterward bent in rolls; they only used the reamer slightly when they had three thicknesses of plate to deal with, as in butt joints with inside and outside covering strips. These works turn out two locomotive boilers every three days. The Baldwin Locomotive Works, which turn out on an average three locomotives per day, punch all their rivet holes one sixteenth inch less in diameter and ream them to driven rivet size when in place. They also use rivets with a fillet formed under head made in solid dies. _Rivets._--Rivets of steel or iron should be made in solid dies. Rivets made in open dies are liable to have a fin on the shank, which prevents a close fit into the holes of the plates. The use of solid dies in forming the rivet insures a round shank, and an accurate fit in a round hole. In addition, there is secured by the use of solid dies, a strong, clean fillet under the head, the point where strength is most needed. Commencing with a countersunk head as the strongest form of head, the greater the fillet permissible under the head of a rivet, or bolt, the greater the strength and the decrease in liability to fracture, as a fillet is the life of the rivet. If rivets are made of iron, the material should be strong, tough, and ductile, of a tensile strength not exceeding 54,000 pounds per square inch, and giving an elongation in _eight inches_ of not less than twenty-five per cent. The rivet iron should be as ductile as the best boiler plate when cold. Iron rivets should be annealed and the iron in the bar should be sufficiently ductile to be bent cold to a right angle without fracture. When heated it should be capable of being flattened out to one-third its diameter without crack or flaw. [Illustration: FIG. 15. Solid Die Rivet.] [Illustration: FIG. 16. Open Die Rivet.]