An Allen screw is a fastener with a six-sided recess in the head (an internal hex drive). It’s tightened with a hex key, hex bit, or driver, making it great for tight spaces and clean, low-profile installs.

• Common uses: Door handles, faucets, light fixtures, furniture, and equipment repairs.
• Why people choose them: The internal hex helps reduce slipping and can allow controlled torque.
• Types you’ll see: Socket head cap screws, button head, flat head, and headless set (grub) screws.

Product pages typically list thread size (metric or SAE), length, and material so you can match what you need for your project.

The name “Allen key” comes from early U.S. manufacturing history, where the term was trademarked and popularized for hex-shaped wrenches used with internal-hex fasteners. Over time, it became a widely used generic term.

• Also called: Hex key or hex wrench—same tool, different names.
• What it fits: Fasteners with an internal hex socket, often described as “Allen” or “hex socket” screws.

When shopping, you’ll often see “hex key” and “Allen key” used interchangeably on product pages and kits, so focusing on the drive size (e.g., 3 mm, 5/32 in) is the best way to ensure compatibility.

“Hex” describes the six-sided shape. In fasteners, it can mean two different things:

• Internal hex (Allen): Screws driven by a hex key/bit. These include socket head cap screws and set (grub) screws.
• External hex: Bolts or screws with a hex-shaped head turned with a wrench or socket.

On product pages, look for wording like “hex socket,” “Allen,” or “internal hex” to identify Allen-style fasteners. If you see “hex head,” that usually means an external hex you’d turn with a wrench. Checking the drive type in the description helps you pick the right tool and compatible hardware.

It’s often called a hex socket screw because it uses an internal hex drive. The exact name depends on the head style and purpose:

• Socket head cap screw: Cylindrical head with an internal hex.
• Button head socket cap: Low, rounded head for a smoother look.
• Flat head socket cap: Countersinks for a flush finish.
• Set (grub) screw: Headless, typically cup-point, used to secure knobs or collars.

All of these are tightened with a hex key/bit. When browsing, match the head style, thread size, and material to your application.

Start by identifying what you had, then filter your options accordingly.

1. Confirm the standard: Metric (e.g., M4, M6) or SAE (e.g., 1/4-20). A sample or the original kit chart helps.
2. Measure size: Diameter and thread pitch, plus length under the head (or overall for set screws).
3. Match the style: Socket head, button, flat head, or headless set (grub). Check point type (cup, flat, cone) for set screws.
4. Choose material/finish: Stainless steel for general corrosion resistance; alloy steel with black oxide is common indoors.

Comparing your sample to the size details and charts on product pages can help you find a close match without overbuying.