Next time you look at a clock with Roman numerals, look closely. Odds are, it will use IIII instead of the more normal IV. Although there are many suggested explanations for this, no one really knows why. However, here are some of the most common ones:
Many clocks use IIII because that was the tradition established by the earliest surviving clock.
Others say that it's because IV represented the Roman God Jupiter, so they avoided using that on clocks.
It's said that Louis XIV, King of France preferred IIII to IV, and asked his clockmakers to use it instead.
It might also be that it's for symmetry. IIII on one side, with IV on the other. There's also radial symmetry because the I would only appear in the first 4 hours of the clock, the V only in the next four hours, and the X only in the last 4 hours.