Sockets go hand-in-hand with ratchets. A socket attaches to the end of a ratchet and fits over nuts and bolts. Socket wrench sets include several small sockets that attach to standalone ratcheting wrenches to save space and money. Some sockets each fit a single bolt head size, and it’s important to have a metric and a standard socket set. Metric sockets are especially useful for automotive applications since imports use the metric system. Socket sets in the standard range of sizes are often referred to as “fractional.”