It fits change in. Bicycle keys as well. But that's not what that bag is meant for. A pair of jeans is not complete without a small, flat pocket just above the right side pocket on the front. The pouch is impossibly small, sometimes only two fingers fit in. What is this bag for, and why don't you see #spijkerbroek Without it?

The best guess of jeans wearers for whom this pouch is an everyday phenomenon does not give the right answer. - Little change? Bicycle keys? They fit in, yes, but that's not what the bag was originally intended for. A search on the internet quickly provides the right answer: it is a storage place for a pocket watch. The old-fashioned clock on a chain disappeared, but the bag remained.