Router bits come in a wide variety of sizes, but they typically use one of two common shank diameters: 1/4-inch or 1/2-inch. The router bit shank refers to the part of the bit that fits into the collet. This is the long, cylindrical part of the bit. Depending on how large of a cutting bit it comes with, it may influence the size of the shank needed to support it. A bigger cutting end may need a larger 1/2-inch shank while smaller bits may use a 1/4-inch. However, you can find most router bits available in both shank sizes. You can find small routers that only accept 1/4-inch shanks while many larger options feature an interchangeable collet so you can use both 1/4-inch and 1/2-inch shanks. 1/2-inch bits offer greater stability and less vibration. You can often find these used with larger bits as they’re less likely to bend or break.