I assume it's like a lot of things where the seller/manufacturer is just lying a little to make their product seem better than it is. Like how if you buy 8gb of ram you don't actually get all 8gb, or if you get a 500gb hdd you don't actually get to use all 500gb, or to use a cycling reference, some manufacturers have sold 23mm wide tires as 25mm tires so that people who really wanted 25mm tires would see those and think they were made of better, lighter material(when in reality they were just skinnier).

Perhaps the stones start as thick and are then thinned as they're shaped.

Or perhaps you just got jipped.

Choose your favorite

I know this is a little old, but I was first interested in the comment about the stones and then I couldn't help but notice this common misconception about storage sizes.

For some reasons, manufacturers count that a gb has 1000 mb, has 1000 kb, has 1000 b, while what we use everyday is a gb has 1024 mb, has 1024 kb, has 1024 b.

So if we take your 500 gb example, you can convert it in the following way:

500 * 1000 * 1000 * 1000 = 500 000 000 000 bytes, this is the amount of bytes in your 500 gb drive.

Now let's see how this translates in real life gb:

500 000 000 000 / 1024 / 1024 / 1024 = 465,66 gb

similarly, a 1 tb drive is considered to have 1000 gb, and turns out being 931 gb in real life units.

They don't lie, but they use different conventions and it is confusing and misleading.

The seller advertised them as being 22mm x 9mm.
The actual size (I measured 10 end to end and divided by 10) is White 21.4 x 8.0; Black 21.8 x 7.7 mm.
The diameter is fine, but the thickness is definitely skimpy compared to the manufacturer's description.