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Its shape is roughly cylindrical with between three 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 many versions, as the barrel shape allows easier construction of odd-sided dice. They have triangular, rectangular, or ovoid faces and rounded or pointed ends to ensure the die lands on a face. A more-common 4-sided barrel die, having rectangular faces much like a dreidel and often referred to as a "long die", is used in the traditional games daldøs and dayakattai. This 4-sided barrel die is easier to roll than the normal tetrahedral d4 used in many role-playing games.
A barrel die is rolled longitudinally so that one of the numbered faces comes to rest on top.
The cricket game Owzthat uses barrel dice which were essentially short lengths of hexagonal bar (i.e. with 6 rectangular faces). The dice were rolled, rather than thrown, and there were no special precautions to prevent the dice landing or stopping end-on.