What Are Woodruff Keys and Why Do They Matter?

Sometimes the smallest parts do the most important jobs.

Take the Woodruff key. It’s a small, half-moon-shaped piece of metal that sits in a shaft and locks rotating parts — like gears or pulleys — in place. Without it, those components would just spin freely, and nothing would turn the way it should.

So why are Woodruff keys used instead of a standard straight key?

• Self-aligning: Their curved shape makes them easier to fit and helps components seat correctly.

• Better load distribution: They spread the force more evenly, reducing stress on the shaft.

• Easy replacement: If something wears out, the Woodruff key can usually be swapped without major effort.

You’ll find them in all sorts of places: automotive engines, motorcycles, lawnmowers, and industrial machinery. They’re one of those small but vital parts that most people never notice — until one goes missing.

At Selo, we stock both metric and imperial Woodruff keys, so whether you’re working on a modern machine or restoring older equipment, you’ll find the right size here. And as always, there are no minimum quantities — whether you need one key for a repair or a pack to keep on hand, we’ll get it sorted.

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