Why the Popular Lubricant Is Called WD-40—and Not WD-50 or WD-100

Anyone who owns a car has probably come across a can of WD-40. For veteran motorists, it’s practically a universal fix—it frees rusted nuts and bolts, chases moisture out of electrical components, and generally solves problems you didn’t even know you had. But why does this iconic lubricant carry the name WD-40?

Why “WD-40,” and not “WD-60,” “WD-100,” or something even higher? Technical products rarely get numbers at random, and this one is no exception. To start, the “WD” part stands for “Water Displacement”—with “displacement” meaning pushing out or moving aside moisture.

What many people don’t realize is that WD-40 was originally developed in the United States not for everyday use, but strictly for military applications. It was created to protect Atlas missiles from corrosion. It didn’t take long, however, for engineers to notice that the formula’s impressive qualities could be useful well beyond defense. A few years after it was first developed, WD-40 made its way into auto parts stores.

As for the “40,” the explanation is surprisingly simple. According to the manufacturer’s official account, that number represents the fortieth attempt it took for their chemists to perfect the formula. The product dates back to 1953 and was created by a California company called Rocket Chemical Company.

One more curious detail: the exact formula of WD-40 is patented and kept strictly confidential to this day. A popular myth claims the spray is made mostly from fish oil, but the company firmly denies that story.