Percentile d10s are numbered 10 - 00 and are used in conjunction with a standard d10 die to create a roll of 1 - 100. While there are 100-sided dice, the percentile d10 method is easier to read and is the most common way of creating a 1-100 roll. The percentile die is a part of the traditional 7-dice D&D dice set and several games use the percentile roll as the primary roll in the game, including Call of Cthulhu and Eclipse Phase -- though those games usually include other dice for things like damage rolls.
These dice work as D&D percentile dice, which can be handy during character creation if you are, for instance, following along the Player's Handbook and need to generate a random number between 1 and 100 to figure out what trinket your character carries with him or her.
