What is the metric size of a wrench that is closest to 1/2 inch?

To determine the closest metric size to a 1/2 inch wrench, it's essential to convert inches to millimeters, knowing that 1 inch is equal to 25.4 mm. Therefore, a 1/2 inch measurement converts as follows:

1/2 inch = 0.5 inches × 25.4 mm/inch = 12.7 mm.

Now, considering the available choices, the metric wrench size that is nearest to 12.7 mm is 13 mm.

This reflects a common conversion where metric sizes are often rounded to the nearest whole number, and in the context of tool usage, many professionals will choose a 13 mm wrench when a 1/2 inch is called for.

The selection of 13 mm as the closest size makes it practical for use in situations where precise measurement is less critical than accessibility and availability of tools. Therefore, selecting this size allows for effective operation while ensuring reliability in common mechanical applications.