Tools that have been bought:

• in sets. Some sizes in the set have never been used since purchase. e.g. drivers, drill bits, sockets, spanners, hole saws. 
• just in case they might be needed to complete a current task but it has turned out that they haven't been needed.
• in preparation for a future project or to kit out a workshop.
• as consumables e.g. drill bits, saw blades.

No regrets though, the whole thing about tools is that they are there if needed.

Like set of spanners that contain a 15mm one. Why? Has anyone ever needed a 15mm spanner (or socket)?

I use most of my tools at least once. That's why I bought them. As it can often be only once, I now have a policy ot borrowing a tool if I can the first time and buying the second time I need it. Try to keep the addiction to buying tools at bay.

The only tool I can think of that's neve been used is a 16 ton hydraulic crimper. I was going to make a DC charger for my electric motorbike (using 2 x 48V 2kW server rack power supplies) and needed this to crimp the high current connectors. I was knocked off the bike before I ever got started on the project. It wasn't an expensive tool but is big and bulky and takes up shelf space. Plus, you never know when you might need it one day...

If you can count dev kits as tools, I would say the tool I bought and never had the opportunity to work with is the "EFR32xG24 Explorer Kit."


A few years ago, the Matter standard started gaining traction, and this kit was a low-cost option to serve as a Matter device. I got two of this kit to explore the matter support. I wanted to connect the kit with my Amazon Echo dot which will act as thread border router and control the device locally. Unfortunately, my Echo device could not connect to the kit no matter what I tried. I wrongly concluded that the kits might be defective.

Later, Element14 announced the Arduino Matter road test, which uses the same chip in an Arduino Nano form factor where we had some discussions regarding how to configure the thread border router (Including Raspberry Pi). Only then did I realize that Echo Dot is not equipped with a chipset that supports thread protocol and can't be used as thread border router. The problem was not with the kits, I had simply tried to use the wrong Echo device as a border router.
And now those two kits are sitting idly somewhere in the racks.

Some others to add to that list:

• Tool upgrades. Sometimes I've upgraded basic tools to 'comfort handles' e.g. if I've needed to do a lot of crimping in one session.
• Backup tools. If working on a tight schedule / on location / at height then I've sometimes bought duplicates just in case a tool gets lost/damaged.

That is a great idea. I used a similar plan a couple of times where I bought a tool (like a Sheetrock lifter) where I used the tool and then turned around and sold it. The difference between the purchase price and what I sold it for was far less than the rental fee would have been. It would have been nice if I knew someone who could have loaned it to me.

For what it's worth I used the link you provided above to apply for a chance of getting a free board.

I bought a DVM that I have never even turned  on (does that count as a tool?) - I bought it because at the time I couldn't believe anyone could sell a new DVM for $5. Needless to say I have much better meters and don't have any real use for this meter. I might build it into a project that needs a voltmeter function at some point, maybe a power supply with built-in DVM.

I once built a frequency counter, because I didn't have one, and it seemed like my lab should have one, and I couldn't justify buying one, but I don't think I ever actually used it beyond testing to make sure it worked. I now have an oscilloscope and signal generators that have frequency counter functions that are at least as good as the one I built.

This evening I will root through my tool boxes to see if I have any weird hand tools that I never use.

Bought a new calculator once used it a few times and kept reaching for my old one, never got used to it.

  The 15mm socket fit the oil pan drain plug on last car I owned.