Whether you’re cleaning your kitchen after a big meal or finishing a painting project, it can be tempting to pour just about anything liquid—or sometimes even solids—down the drain.

The mystery of the lock nut, though, isn’t how it works. The nylon insert is just a little too small for the bolt, and the bolt, being harder than nylon, taps a very close-fitting hole in the ...

Unless you are a mechanical engineer, you might not realize there’s a lot of nuances to something even as simple as a nut and bolt. How many threads do you need to engage? Do lock washers work?