Designed for construction, these metric screws are often used to join I-beams and scaffolding. They’re Class 10.9 steel, which is at least 25% stronger than medium-strength steel. Since the head is 10% wider than a standard hex head, it spreads force over a larger area, and you can tighten these screws with more torque. They also have a precisely measured unthreaded section under the head, called a grip. It’s stronger than the threaded section, so you can place it in joints exposed to sideways force. All screws meet EN 14399 (formerly DIN 6914 and ISO 7412) standards for dimensions. Length is measured from under the head.

Steel screws are best for dry environments, since moisture will cause them to rust. They don’t have a finish, so they’re easier to paint than hot-dipped galvanized steel screws. To meet structural standards, use them with plain steel structural hex nuts and washers.

Hot-dipped galvanized steel screws are 10 times more corrosion resistant than zinc-plated screws, so they resist rust in wet areas. The finish is thicker than other finishes, so these screws are compatible with only hot-dipped galvanized steel fasteners. To meet structural standards, use them with hot-dipped galvanized structural hex nuts and washers.