Avoid Common Hex Key Mistakes for Precise Fastening

Publish Date: January 28, 2026 | Category: Hex Keys | tags: hex keys

Not all threaded fasteners have a traditional slotted or Phillips drive type. You can find them in a wide range of alternative drive types, such as hexagonal socket.

Hexagonal socket fasteners are characterized by a six-sided drive recess. In the center of the head is a shallow hexagonal cutout. For hexagonal socket fasteners such as this, you’ll need to use a special tool known as a hex key. Consisting of an L-shaped piece of metal with six sides, hex keys are designed to tighten and loosen hexagonal socket fasteners. Here are some common mistakes to avoid when using hex keys.

Using an Undersized Hex Key

Don’t make the mistake of using an undersized hex key. Hex keys are available in both SAE and metric sizes. Common SAE sizes include 1/8″, 5/32″ and 3/16″, whereas common metric sizes include 2.5mm, 3mm, 4mm, 5mm and 6 mm. Whether SAE or metric, though, hex keys need to fit snugly in the hexagonal recess of the fastener with which they are used. If a hex key is too small, it won’t be able to grip and turn the fastener.

Non-Perpendicular Angle

Another common mistake to avoid is inserting a hex key at a non-perpendicular angle. Hex keys should be inserted so that they are perpendicular to the fasteners with which they are used, resulting in a clean 90-degree angle. Inserting a hex key at any other angle may damage the fastener’s hexagonal recess when you turn it.

Using a Worn or Damaged Hex Key

If a hex key is worn or damaged, you may need to replace it. Hex keys work by gripping the six sides of a fastener’s hexagonal recess. Over time, hex keys can become smooth. Rather than featuring six sharp sides, a hex key may become smooth and rounded from regular use. When this occurs, it may fail to grip and engage a fastener’s hexagonal recess.

Partial Seating

Hex keys need to reach the bottom of the fastener’s recess. If a hex key is only partially seated, it won’t offer full engagement. The end result is an increased risk of cam-out. As you attempt to turn the hex key, it will slide up and out of the recess rather than tightening the fastener. You can avoid this problem by inserting the hex key all the way to the bottom of the fastener’s hexagonal recess.

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