U.S. metal fabricators still juggle inches and millimeters decades after the Metric Conversion Act of 1975. The law made adoption voluntary, leading to President Reagan disbanding the Metric Board in 1982. Today, companies like Caterpillar and General Motors use metric for global trade, but many domestic clients provide drawings in U.S. customary units.

This dual-system reality creates tangible costs. Pat Naughtin estimated annual losses at $1.28 trillion in 2008 (roughly $1.86 trillion today) from conversion errors, dual inventories, and lost international business. A machinist's post about a plate needing both 4.5-inch dimensions and 40 mm bores illustrates the daily friction.

Progress continues slowly. Schools teach metric in science, and more manufacturers switch for long-term savings. The U.S. already defines customary units via metric standards since 1893, making a full shift technically feasible. The challenge remains cultural and political, not technical.