Orbiforms have the same width in every direction. If you put a book on three of these it will roll smoothly on the table, just as a book on three spheres would. So, unlike conventional tetrahedral four-sided dice, these dice roll smoothly on the table and come to rest showing one of the four numbers.
The shape is mathematically fair, giving equal probability for the four results. Measuring 1¹⁄₁₆ inches (29 mm) in diameter, the Orbiform d4 comes in a set of three, so you can roll them between two planes and check their constant width property (or use them as dice if you really want).
Pack of 3.
Price = (the 357th prime number) pence = 2399 pence = £23.99