One Good Turn: A Natural History of the Screwdriver and the Screw (6 page)

The Dresden suit is identified as jousting armor. Jousting, or tilting, originated in martial tournaments in which groups of mounted knights fought with lance, sword, and mace. By the sixteenth century, this rude free-for-all had evolved into a highly regulated sport. Two knights, each carrying a twelve-foot-long blunted wooden lance, rode at each other on either side of a low wooden barricade called the tilt. The aim was to unseat the opponent, have him shatter his lance, or score points by hitting different parts of the body. To protect the wearer, jousting armor was heavily reinforced and weighed more than a hundred pounds (field armor was lighter, weighing between forty and sixty pounds).

The black Dresden armor was for the
scharfrennen,
a
particularly deadly German form of joust fought with sharpened lances and particularly popular with young men. Such combat required additional protection. The helm, called a
rennhut,
covered only the head and upper part of the face. The lower part of the face and the neck were protected by the
renntartsche,
a large molded plate that extended down to cover the left shoulder and was attached to the breastplate. A small shield, called a tilt targe, was fastened to the breastplate. Such “target” pieces were designed to fall off when struck; sometimes they were fitted with springs that caused them to fly dramatically into the air to the delight of the wildly applauding spectators.

Like most of the armor in the gallery, the steel plates of the Dresden suit are held together by rivets and buckled straps. Then I notice something: the
renntartsche
is screwed to the breastplate—the slotted heads, about half an inch in diameter, are plainly visible. Armorers, too, used screwdrivers! Since armor plate is relatively thin, these screws are probably mated with nuts, although I can’t see them since they are hidden inside the suit. The Greenwich Armory outside London employed a dozen or more general armorers as well as a variety of specialists such as platers, millmen, helmsmiths, mail-makers, and locksmiths. It was probably the latter who fabricated the screws (medieval locks sometimes used threaded turning mechanisms).

We can be fairly sure how these screws and nuts were fabricated. In
Mechanick Exercises,
Moxon includes a section titled “The Making of Screws and Nuts,” a process that could not have changed much since the Middle Ages. He describes how, after the head and shank are hammered out of a forged blank, the “screw-pin,” that is, the thread, is cut with a die called a screw plate. The screw plate, made of tempered steel, has several threaded holes of different diameters. The blank is placed in a vise, and the screw plate is forced down hard and turned to cut the threads. (The corresponding nut is threaded with a tap, a tapered screw fitted with a handle.)
“Screw
the
Nut
in the
Vise
directly flat, that the
hole
may stand upright, and put the
Screw-tap
upright in the
hole;
then if your
Screw-tap
have a
handle,
turn it by the
handle
hard round in the
Hole,
so will the
Screw-tap
work it self into the
Hole,
and make
Grooves
in it to fit the
Threds
[
sic
] of the
Screw-pin.
”
¹³
Moxon’s complicated instructions underline the combination of delicacy and brute strength that was needed to make a screw in this fashion.

Looking more closely at the Dresden armor, I see that the helm is attached to the backplate by large wing nuts. Since the highest points in a joust were accorded to a hit to the helm, special precautions had to be taken to protect the head. Field helms were close-fitting and worn over a coif of chain mail; the heavy jousting helm, on the other hand, did not touch the head. It was
supported on the shoulders like a modern deep-sea diver’s helmet and attached to the breastplate and backplate with leather straps to keep from getting knocked off. “In suits for the joust or tourney these adjustable fastenings could not always be depended upon,” observes Charles Ffoulkes in a
1912
book on armor, “and the great helm . . . [was] often screwed on to the suit.”
¹⁴
Wing nuts, such as the ones on the Dresden armor, were a later refinement that allowed the exact angle of the helm to be closely adjusted. This was important. The so-called frog-mouth helm had a narrow, beaklike viewing slit, designed so that the knight could see out as he leaned forward in the saddle, riding toward his adversary. At the last minute, just before the moment of impact, he would straighten up and the lower part of the helm would protect his eyes from stray splinters. It required nerve: galloping down the list, aiming the heavy lance at one’s opponent who was barely visible through the helm’s shaking, narrow slot, then sudden darkness followed by the jarring crash of wood against steel.

Bracket for jousting helm and protective
renntartsche,
Dresden, sixteenth century.

Multipurpose armorer’s tool, sixteenth century.

It is unclear exactly when screws were substituted for straps. Ffoulkes refers to a French military manual, written in
1446
, that provides a detailed description of jousting armor. The text refers to most attachments as
cloué
(literally “nailed,” as rivets were called arming nails), but in one place describes a piece as being
rivez en dedens
(fixed from the inside), which sounds like a screw and nut. I came across references to helms being screwed to breastplates as early as
1480
.
¹⁵
The oldest screw in the Metropolitan Museum is part of a steel breastplate that is identified as German or Austrian and
dated
1480
–
90
. If screws were used in the
1480
s, that would make them the same age as the screws in the matchlock in
Pollard’s History of Firearms
and the metal screws in the
Housebook.
Ffoulkes describes the heads of the screws as square or polygonal. However, all the screws I saw at the Metropolitan were slotted.

I look through Ffoulkes’s chapter on “Tools, Appliances, Etc.” According to the author, few armorer’s tools have survived. He describes a display in the British Museum: “In the same case is a pair of armourer’s pincers, which resemble the
multum in parvo
tools of today, for they include hammer, wire-cutter, nail-drawer, and turnscrew.”
¹⁶
He refers to a photograph. Excitedly, I turn to plate V.
¹⁷
I had missed it earlier. Upon closer examination I can make out what looks like a pick at the end of one handle, and at the end of the other—a flat screwdriver blade. The caption beneath the photograph gives the date as the sixteenth century.

Another combination tool. I am disappointed that the oldest screwdriver resembles the kind of gimcrack household gadget that is sold by Hammacher Schlemmer. Although Ffoulkes calls this a turnscrew, like the screwdriver blade that was part of the arquebusier’s spanner, it probably didn’t have a special name. With so few screws, all that was needed was a part-time tool.

I
N SEARCHING FOR
the first screwdriver I have become interested in screws. When Agricola compared the screw to the nail as a way of constructing bellows, he observed that “there is no doubt that it [the screw] surpasses it in excellence.”
¹
In fact, the wrought-iron nail is a remarkable fastener. It bears little resemblance to the modern steel nail. The modern nail is round and pointed and forces itself between the wood fibers. Such nails are reasonably effective when driven into softwood (spruce, pine, fir), but will usually split hardwood (maple, birch, oak). Moreover, even in softwood the holding power of a round nail is weak, since it is kept in place only by the pressure of the fibers along two sides. The wrought-iron nail, on the other hand, is square or rectangular in cross-section with a hand-filed chisel point. The chisel point, driven across the grain, cuts through the wood fibers rather than forcing its way between them, just like a modern railroad spike. Such nails can be driven into the hardest wood without splitting it, and they are almost
impossible to remove, as I discovered when I nailed a replica wrought-iron ship’s nail into a board as an experiment.
^I

Wrought-iron nails have limitations, however. If they are driven into a thin piece of wood, such as a door, their holding power is greatly reduced and their protruding ends must be clenched—bent over—to keep them fast. Wrought-iron nails are most effective—and easier to fabricate—when they are relatively large (at least an inch or two long). That is why the earliest screws replaced nails in small-scale applications such as fixing leather to a bellows board, or attaching a matchlock to a gunstock. Even a short screw has great holding power. Unlike a nail or a spike, a screw is not held by friction but by a mechanical bond: the interpenetration of the sharp spiral thread and the wood fibers. This bond is so strong that a well-set screw can be removed only by destroying the surrounding wood.

The problem with screws in the sixteenth century was that, compared to nails, they were expensive. A blacksmith could turn out nails relatively quickly. Taking a red-hot rod of forged iron, he squared, drew, and
tapered the rod to a point, pushed the reheated nail through a heading tool, then with a heavy hammer formed the head. The whole procedure, which had been invented by the Romans and was still used in the
1800
s (Thomas Jefferson’s slaves produced nails this way at Monticello), took less than a minute, especially for an experienced “nailsmith.” Making a screw was more complicated. A blank was forged, pointed, and headed, much like a nail, but round instead of square. Then a slot was cut into the head with a hacksaw. Finally, the thread was laboriously filed by hand.

Gunsmiths manufactured their own screws, just as armorers made their own bolts and wing nuts. What about clockmakers? Turret clocks appeared in Europe as early as the fourteenth century. The oldest clock of which we have detailed knowledge was built by an Italian, Giovanni De’Dondi. It is an astronomical clock of extraordinary complexity. The seven faces show the position of the ancient planets: the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn; in addition, one rotating dial indicates religious feast days, and another displays the number of daylight hours in the day. De’Dondi fashioned the bronze, brass, and copper parts by hand. It took him sixteen years to build the clock, which he finished in
1362
. Although the original was destroyed by fire in the sixteenth century, the inventor left detailed instructions, and two working replicas were
built in London in
1962
. One of these now belongs to the National Museum of American History, and I catch up with it in Montreal, where it is part of a temporary exhibit. The exquisite seven-sided machine stands about four feet tall; the gearwheels are driven by suspended weights. I examine the mechanism. As far as I can see, all the connections are pegged mortises and tenons, a detail adapted from carpentry. The projecting tenons have slot-holes into which a wedge is driven. These wedges vary in size from tiny needlelike pins to one inch long. There must be several hundred such attachments, but I can’t see a single screw.

According to
Britten’s Old Clocks and Watches and Their Makers,
the standard work of horological history originally published in
1899
, “screws were entirely unknown in clocks before
1550
.”
²
Their introduction was a result of the demand for smaller and lighter domestic clocks, especially watches. According to
Britten’s,
“Even the earliest watches generally possess at least one screw. These screws have dome-shaped heads and the slots are V-shaped. The thread is coarse and irregular.”
³