ITEM: Eye­glasses screw

IN­VENTED: 20th cen­tury USE: Join­ing hinges

Popular Science - - SMALL WONDERS -

Lon­don op­ti­cian Ed­ward Scar­lett was among the first to advertise tem­ple arms for eye­glasses around 1730. Later ap­pendages fea­tured a door­like hinge that let users fold their specs for travel. The first models used metal posts to af­fix frames to arms. But, as the re­fine­ment of in­dus­trial thread­ing ma­chines like lathes con­tin­ued into the 20th cen­tury, tiny stain­less-steel screws took that job. Over time, the fit has be­come stan­dard­ized: Most frames now re­quire fas­ten­ers with a shaft di­am­e­ter of 1.4 mm, while some thin wire frames use ones as small as 1.2 mm. Con­sider that two-thirds of Amer­i­can adults—about 159 mil­lion peo­ple—wear pre­scrip­tion glasses. That’s a lot of screws that could go loose. For­tu­nately, you can find a re­pair kit at nearly any drug­store.

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