In the past I've used 3-in-1 multi purpose oil, like this

WD-40 is more of a solvent than a lubricant:
https://lifehacker.com/5891936/when-should-i-not-use-wd-40

3-in-one oil is very good too, comparable to sewing machine oil.

On this subject, I have an old hard drive which works OK but makes a horrible squealing sound as it spins. How do I lubricate this? I'm frightened of breaking something so haven't attempted anything yet.

I'm not aware of any way to safely lubricate a hard drive. Just gotta deal with the noise. 😉

clueless1 wrote:

WD-40 is more of a solvent than a lubricant:
https://lifehacker.com/5891936/when-should-i-not-use-wd-40

3-in-one oil is very good too, comparable to sewing machine oil.

How about shaver/clipper oil?

That should work good too. Any light-colored mineral oil, from what I understand.

REMVING POST FOR MY OWN SAFTY

Errius wrote:

On this subject, I have an old hard drive which works OK but makes a horrible squealing sound as it spins. How do I lubricate this? I'm frightened of breaking something so haven't attempted anything yet.

9 times out of 10, hard drive noise is caused by the heads dragging on the platters. I like to take the cover off the drives and give the platters a nice scrub soap, water and a scouring brush (the more abrasive the better; you want to get *all* the oxide off those platters). Then you spread a *thin* layer of oil over the platters (10w40 non-detergent motor oil works well, though read/write speeds will be a little slow until the drive warms up and the oil thins out). Then you just reassemble the drive and you’re all set!

I recommend performing this procedure in a humid bathroom with a hairnet and powder free gloves on, as you don’t want any dust or hair getting inside the drive.

(Seriously, nobody do this. You *will* ruin the drive. This above portion of this post is just a joke! I shouldn’t have to say this, but I’ve seen people take some crazy things seriously on forums over the years...)

Serious Answer: If the bearings are going bad in a HD, you’re out of luck, unless you have access to a clean room that is. (Even then it’s tough.)

It sounds like someone is murdering cats next to me.