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.]