Its shape is that of a cylindroid with between four and twenty flattened triangular facets, each numbered. Each triangular face alternates in alignment about 180 degrees. The two ends of the cylindroid are formed by half as many triangular facets as there are numbered faces, and are arranged so that it is impossible for the die to stop on one of its 'ends'.
There are six versions: 4, 6, 8, 10, 12, and 20 sides. They all have triangular faces except the 4 sided one, having rectangular faces much like a dreidel. The 4 sided barrel die is easier to read than the normal tetrahedral d4 used in most role-playing games and is favored by many gamemasters.
A barrel die is rolled longitudinally so that one of the numbered faces comes to rest on top.
Barrel dice are manufactured by games company Crystal Caste under the trademark Crystal Dice and sold by games shops and games websites worldwide.