National Geographic : 1940 Dec
Photograph from United Aircraft Corp. Harvest of Horsepower! Like Ripened Grain Thousands of Airplane Cylinders Stand Ready for Assembly Linings of many airplane cylinders must be harder than glass to withstand wear and be honed to an accuracy equal to1/10 the thickness of aspider thread. Such precision enables engines to run 600 hours or 100,000 miles without a major overhaul.