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I acquired a bunch of camping gear from a friend who moved out of the country. There was one of these hockey puck shaped disks, half grey half black, remaining in the cooking gear, but I have not a clue how to use it, and the friend is out of contact for a few months. I tried holding a lighter to it, expecting it to be some kind of cooking charcoal pellet, but it didn’t catch on fire. How do I use it? Or is it for something else entirely? I googled and googled and can’t figure out what it is used for.

  • 9
    It the remains of whatever they cooked last... Jun 23, 2018 at 19:29
  • 1
    Does it look similar to this product: amazon.com/dp/B000B8FW0Y?
    – jkd
    Jun 24, 2018 at 0:38
  • 16
    If you don't know what it is, set it on fire. I don't know you and already think I like you :)
    – Peter
    Jun 25, 2018 at 10:27
  • 6
    "I have not a clue how to use it" ... so ... "I tried holding a lighter to it". That just made my day!
    – berry120
    Jun 25, 2018 at 14:17

4 Answers 4


It looks like a grindstone. The two halves would be different fineness. Your friend probably had this in his cooking kit to sharpen knives.

This doesn't look like it has anything to do with starting fires.

Here is a device that looks very similar to yours. It's clearly for sharpening:

enter image description here

This is a snippet from the web site of Sharpening Supplies.

  • 7
    Ah sure enough! Hah that’s funny. Thanks all!! I was convinced it had to do with fire as it was kept inside this cooking apparatus. My next step was to soak it in gasoline and try lighting it because it had a faint smell of oil to it. Now that i’ve read about these, i guess it’s common to oil them up a bit for sharpening. Jun 24, 2018 at 14:28
  • 11
    Technically it's a whetstone, not a grindstone. A grindstone is typically wheel-shaped and turns on an axel. See grindstone vs whetstone. Same function, different mechanism.
    – Pharap
    Jun 24, 2018 at 17:51
  • 2
    Did you actually soak it in gasoline? If so, I think it might be permanently ruined.
    – stannius
    Jun 25, 2018 at 18:20
  • 1
    If you were going to soak it in anything you'd want to use something a whole lot less aromatic than gasoline, like kerosene or diesel fuel. Jun 25, 2018 at 22:18

There are two possibilities.

  1. As Olin Lathrop states it's a grindstone, and would be used to sharpen, or "file" things. It that's the case, then you would not use it to start a fire.

  2. It's part of a fire starting kit. I say a part, because fire starting kits usually have something like flint, that you would strike against something like a steel part. Flint can come in many colors but it's usually black or brown, and not gray. Also, the shape is generally not that uniform, and it's usually nowhere near that big.

If your 100% sure that it's a fire starting device, then it's probably flint. Though I would sooner think it's a grindstone, or even just a weight to keep the paper napkins in place.

A bit of bonus advice. Never try to light something on fire if you don't know for sure what it is.

  • 6
    Yeah... Please don't put a fire to an unknown object. It could be explosive and you would've lost at least one of your hands
    – Nelson
    Jun 24, 2018 at 5:54
  • 4
    @Nelson I wouldn't say an explosive - after all, the likelihood is quite small. Rather, I'd warn against highly flammable objects and/or materials - not only do you risk burns, but also a wildfire or property damage. Or things that burn so brightly that they damage your eyes.
    – user15927
    Jun 24, 2018 at 14:01
  • 1
    Yeah with this particular friend maybe there was significant risk of that decision being dangerous ;) Jun 24, 2018 at 14:26
  • 2
    I should have mentioned i ground a bit off and tried lighting that first. Although i do regret trying to light the disk afterward. Could have been an unusual firework round for all i knew at the time. Jun 24, 2018 at 14:32
  • 1
    "Never try to light something on fire if you don't know for sure what it is." That sounds like exactly the opposite of OP's flowchart... "Found object: Do you know what it is? No: try to light it on fire." Seriously though, if you took something out of my big bag of car-camping fire starting supplies and randomly tried to light it too close to the rest of the stuff... wow, this makes me wonder if I should be more careful about storing my fire starting stuff. Nothing explosive, but when you have a bunch of kindling materials, fatwood sticks, charcoal, etc. all together... let's rethink this.
    – Loduwijk
    Jun 25, 2018 at 20:54

It's a sharpening stone. Very nice, but unless you're really good at sharpening knives, etc, by hand you'd be better off with a ceramic rod sharpener, which is sufficiently easy to use that even a complete dodo like myself can put a wicked edge on a knife with it.

I've got an old-old-old Smith's ceramic rod knife and scissor sharpener that works really well. It looks like the more up-to-date version is the model 50185, which you can find many places, including Amazon.

Best of luck.

  • You don't have to be really good at sharpening knives for it to be better than a 10$ sharpening tool! I just use a whetstone and a few (wet) sanding papers - and most likely if you want to sharpen knives for regular use there is no need for the whetstone either. Just use 400 sandpaper and then 1000 sandpaper against the edge at the angle the edge has. You can shave with most knives with just that. And don't put them in the dishwasher.
    – Stian
    Jun 26, 2018 at 9:13
  • It's a $12 sharpening tool. Big difference. BIG difference! :-) But, point taken. When I got married my wife came with a nice set of knives and one of those Smith tri-hone sharpening things with three grades of whetstones, and I dutifully sharpened her knives (usually using only the finest of the three stones). Took about half an hour to get the thing out, find the oil, get out the little angle gauge, sharpen the knives, and put it back. With the el-cheapo rod sharpener I'm done in two minutes, tops, and I, personally, get a better edge that way. YMMV. Jun 26, 2018 at 12:32

[Edit]I believe Pharap's comment is correct. Also, magnesium would not be used for the striker. There are some firestarter kits that supply a magnesium compound to be used as fuel.

[original reply] The piece you are missing is usually called a striker. It would be a stick or rod, often of magnesium. You (ahem) strike the striker on the stone to make sparks.

  • 1
    I'm pretty confident that it's the wrong kind of stone for a fire striker. The kind of rocks used for fire striking tend to be flaky rather than grainy. Like the ones found in this image. The OP's image looks closer to a whetstone.
    – Pharap
    Jun 24, 2018 at 17:58

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