Si la dificultad consiste en la expresión "inch drive", añado esta referencia en inglés para aclarar su sentido (que ya ha explicado el compañero Raúl Casanova).

http://www.the-crankshaft.info/2010/01/wrenches.html
A variety of %-inch or %-inch drive heads or sockets: The #-inch, %-inch, and %-inch sockets are the ones you'll use the most, unless you need a metric set. The metric sizes most often used are 10,11,12,13, and 14 mm.
The word DRIVE refers to the size of the square hole in each socket where it attaches to the ratchet handle. It's easy to remember that the smaller the drive, the smaller the job you use it for. A M-inch drive is for tiny areas; %-inch drive is for the next range of sizes, typically up to SAE % or 18 mm metric; &-inch drive is for up to SAE IX, or up to 25 mm; and other drives up to 2 inches are for really big jobs (you won't need one of these monsters). You can use adapters to convert sockets of one drive to fit handles of another drive.