There’s a blue and yellow can of it in almost every garage in America. People spray it on squeaky hinges, stuck bolts, bike chains and door locks, sometimes on things it was never meant for. To use WD-40 well, it helps to know what it was actually designed to do.
The name says it all
WD-40 stands for “Water Displacement, 40th attempt.” According to Snopes, which relies on the company’s own history, the formula was created in 1953 at the Rocket Chemical Company in San Diego, and chemist Norm Larsen perfected it on his 40th try. Its first job had nothing to do with doors: it was bought in bulk to protect Atlas missile parts from rust.
That origin explains everything. WD-40 was born to chase moisture away from metal, not to be a grease.
What it’s designed to do
The WD-40 Company describes its classic formula as a blend of lubricants, anti-corrosion agents and ingredients for penetration, water displacement and soil removal. In practice, that means five jobs:
- Displace moisture: it pushes water out of metal parts and tools left in the damp.
- Protect against rust: it leaves a thin film that shields metal from humidity.
- Loosen: it seeps into rusted nuts, bolts and stuck screws.
- Clean: it removes grease, sticky residue and grime.
- Lubricate: lightly. Contrary to a popular myth, it does contain lubricants.
That’s why fall is the perfect season for it: before storing the mower, garden tools or the bike for winter, a light coat protects metal parts from rust.
Where people get it wrong
The confusion comes from that last point. WD-40 lubricates, but with a light, penetrating film. Where a part needs long-lasting lubrication, a dedicated product holds up better. A squeaky hinge is a good test: a quick spray quiets it, but if the squeak comes back after a few weeks, the hinge needs a heavier lubricant.
- Bike chains: the company says WD-40 is a good maintenance product, as long as you wipe off the excess before riding. For long-term lubrication, it points to its specialist bike lube.
- Door locks: home services site Angi notes that regular WD-40 can attract dust and dry out over time inside a lock, and suggests a dry PTFE lubricant or powdered graphite instead.
- Some plastics: the company lists polycarbonate and clear polystyrene among the few surfaces to avoid. Check before spraying clear plastic parts.
The limit
WD-40 is not a miracle product. The company itself debunks two persistent rumors: it doesn’t contain fish oil, and it should not be used for any medical purpose, including arthritis pain. It’s also flammable, so keep it away from flames and heaters, and follow the instructions on the can.
Rust is the main enemy of tools stored for winter: here’s how a permaculture gardener brings rusted pruners back. Before putting the mower away, avoid this common mistake when scraping the deck. And for appliances, the simplest checks are often the best, like the sheet of paper technicians wedge in the fridge door.
Displace water, protect, loosen, clean, and lubricate lightly. That’s the trick.
