alt Hacker NewsWD-40's advantage is that it's not terrible to get on your skin when you're out working, and it's cheap.
The people who use it are looking for cheap, mostly.
Source: farming. We have many different lubes and penetrating products for when we're in the actual shop, but in the field, nothing beats wd-40 for getting back to work fast, or unsticking some shit when all you have is a hammer and you just know when that fucking bolt comes loose it's going to throw rust and dirt all over your face.
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I'm unsure what your definition of "cheap" is for WD-40 but I find it to be very overpriced. If I need a universal lubricant that is readily available and cheap, I just use used motor oil.
Before I got serious with fixing and building things at home, WD-40 was a catchall panacea you sprayed on stuff to make it work.
The caveat is use the right one for the right job. There's a meme that if its not moving but its supposed to you need WD-40... well you need Silicone WD-40 or any silicone based oil like for a garage. If you use regular WD-40 in a garage it is a degreaser essentially, and your squeaking goes away momentarily, and then comes back. After I learned this, you have no idea how much silicone WD-40 I had to put in my garage to make the squeaking stop for good.