The most common type of nut, you'll find hex nuts everywhere—from massive highway bridges to the delicate hinges on eyeglasses. They largely replaced square nuts after World War II, when advancements in technology made cutting nuts into hexagonal shapes easier and cheaper. They’re not as boxy as square nuts, so they take up less space, and with more sides, they're easier to grip with a wrench from many angles.

Available not only in a vast range of sizes, hex nuts also come in dozens of materials to meet the needs of nearly any job in any environment: from steel when strength matters most, to lightweight and corrosion-resistant aluminum, to ceramic that won’t melt in temperatures up to 3000° F.

While hex nuts are the go-to for fastening parts in assemblies, vibration can shake them loose over time. To improve their hold, fasten a thin-profile nut, also called a jam nut, under a standard-height hex nut. For nuts that withstand even higher levels of vibration, consider locknuts.