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Purchased this die from a hobby/tabletop store yesterday, mainly because I thought it looked cool, and that it was funny that it was so hard to read the faces:

shiny gold icosahedron numbered 0–9 twice

I was passively rolling the die, and noticed that my rolls were all very low. Checking the faces, I found that this was actually a d10 with twenty sides and two instances of each number, 0-9.

Is there a name for a die like this? Would I be able to purchase another, possibly with sides 10-20?

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    \$\begingroup\$ I wouldn't be using it to emulate a d20 - I DM games frequently, and have sometimes found the need to "fudge" a roll or two. If I could somehow have a guaranteed way of rolling above ten on a d20, I would rather use that than simply hide the real roll behind my screen. \$\endgroup\$ – Ajohnson Jul 20 '18 at 3:13
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Gamescience, a dice manufacturer, calls such a die simply a d20 0–9 Twice. Yours appears to be this one, and, as of this writing, it appears you can buy more.

However, you may not need to. The owner of such dice usually colors in at least half the numbers himself—wax crayons used to be included with dice sets for exactly this reason, but paint or, I guess, even nail polish works, too—so that to generate a number from 1 to 20, the roller picks either the colored-in or uncolored or differently colored numbers as high. That way an uncolored 0 represents 10 and a colored-in 0 represents 20, for example, and, of course, rolling the same die twice generates a d%.

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As noted in another answer, this is currently called by GameScience a "d20 0-9 Twice". Historically, this is what d20's looked like before the invention of the proper d10. (Note that Platonic solids are only possible with 4, 6, 8, 12, or 20 sides, and these are the entirety of what early dice sets contained.) Indeed, common usage would be to color half the faces in a distinct color to indicate values above 10. Thus, the one die could be used as a d10, d20, and d%. Some old-school gamers still prefer them for perceived elegance and efficiency in this way.

Here are some quotes from the 1E AD&D DMG (1979) on usage of such dice. Note that the modern d10/d% is not included in the illustration, and the d20 (0-9) is referred to as the "standard d20". From the Dice section (p. 9-10):

1E AD&D Platonic-Solid Dice

If a d20 is used either 1-20 (assuming the use of a standard d20 which is numbered 0-9 twice without coloring one set of faces to indicate that those faces have 10 added to the number appearing) or 1-40 (assuming that one set of faces is colored) can be gotten by adding 0 if 1 or 2 is rolled on the d4 and 10 or 20 (depending on die type) if a 3 or 4 is rolled...

The d20 is used often, both as d10 and d20. The bell-shaped probability curves typically range from 2-20 to 5-50, i.e., 2, 3, 4 or 5d20 added together. Also common is the reading as above with one decimal place added to the result to get 20-200,30-300, etc. In the latter case, a roll of 3 on one die and 0 (read as 10) totals 13, plus one place, or 130.

Non-platonic solid-shaped dice are available in some places. The most common of these is a ten-sided die numbered 0-9. As with the d20, this can be used for many purposes, even replacing the d20 if a second die is used in conjunction to get 5% interval curves (1-20). Also, the die can give 0-9 linear curve random numbers, as the d20 can.

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    \$\begingroup\$ I've never heard of using a d4 along with a d20. Circa 1980, when rolling to hit in D&D, we always used a d6 along with a d20. If the d6 showed 4-6, you added 10. There are always lots of d6's around, and a d6 rolls more easily than a d4 and is easier to read. \$\endgroup\$ – Ben Crowell Jul 19 '18 at 21:10
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Others have said what Gamescience calls these. Personally I refer to them as a 20 sided d10. I'm sure if you said that to someone in a dice shop they'd know what you meant.

Here is an article from 2008 referring to to such a die as a "twenty sided d10".

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  • \$\begingroup\$ Rephrase your answer would be extremely valid. That is the name I would use as well... 20-sided d10! \$\endgroup\$ – JP Chapleau Jul 20 '18 at 14:41
  • \$\begingroup\$ I love my 12-sided d4 dice :) \$\endgroup\$ – ikegami Jul 21 '18 at 18:41
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What my fellow old school grognards said. Its called a d20. Since nowadays d20s are numbered 1 thru 20 instead of 0 to 9 twice, different folks call it different things. There is no official name, since it is officially a d20. As noted, GameScience has taken to calling them "d20 0 - 9 Twice." But technically this is still a d20, it's just numbered differently than you're used to. There is no technical name that differentiates it from a d20 numbered 1 - 20.

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    \$\begingroup\$ Really? I'd have called it a d10, because of the range of scores you can get. If the GM told you to roll a d10 (or had to roll a d10 themselves) this would be perfectly acceptable, but not for a d20. Effectively it's a d10 but just looks like a d20. \$\endgroup\$ – colmde Jul 20 '18 at 13:16
  • \$\begingroup\$ "But technically this is still a d20" - I'm not sure where a technical definition of dN would be found but certainly the way I would use it is "a dice used to generate a number from 1 to N" so a isocahedron with 0-9 twice I would call a d10 (on the understanding that 0 = 10) \$\endgroup\$ – Chris Jul 25 '18 at 13:27

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