They are thicker and stiffer than most road rings, but they work with either wide or narrow chain. Double set of mounting holes means they fit either 110 mm or 130 mm bolt circle cranks! They have tall teeth to prevent accidental derailment, and are a great choice for singlespeed or fixed-gear bikes. Available sizes: 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48
This is especially useful if you're using a hub made for a multi-speed freewheel, because it reduces the amount of re-dishing required. These also take up the space formerly occupied by the second chainring, so if you use these, you don't need to buy short chainring bolts...use the same bolts you were using for your double chainring set.