Metric wrenches are sized in?

Metric wrenches are sized in millimeters because the metric system typically uses millimeters as the standard unit of measurement for small dimensions, which is appropriate for tools like wrenches that need to fit specific bolt or nut sizes. The millimeter scale allows for precise sizing and is commonly used in automotive and mechanical applications for its accuracy.

While kilometers, decimeters, and centimeters are also metric units, they are not practical for the sizing of tools, as they are either too large or not aligned with the specifications commonly encountered in wrench sizes. Millimeters provide the right level of granularity, making them the standard in tool manufacturing and measurement.