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BORN 1842Simple as it might seem, the adjustable
wrench is an engineering marvel. Rotate
its screw mechanism with your thumb,
and a series of teeth—called a rack and
worm—open or close the jaw to fit most
any nut or bolt. Credit for this ingenious
idea goes to British engineer Richard
Clyburn, whose cast-iron “screw span-
ner” looks a lot like the do- it- all wonder
in your toolbox right now. Chrome-plated
steel now helps prevent corrosion, and
modern models incorporate one knuckle-
saving improvement: a small tension
spring to prevent slippage as you crank
on particularly recalcitrant fasteners.