It’s fairly common to find that your socket set isn’t entirely complete—it skips one or more sizes. There are two main reasons for this. One is that the missing sockets aren’t commonly used sizes, so by omitting them, the manufacturer can keep the price down a bit while still offering a fairly complete set of tools. The other reason for this common practice is more of a marketing ploy; there’s a good chance you’ll buy the missing sockets individually to complete the set, thus greatly increasing the profits for the manufacturer.