When we use fractions for measurements, the denominator is virtually always a power of two. The only one I can think of that isn't is a fifth of alcohol, which is really just its own unit at this point.
Neither 1/36th or 1/12th are used, and the other two aren't fractions. We don't say six and a twelfth feet, we say six feet one inch. With distance, fractions are only used for fractions of an inch (apart from trivial uses like "one and a half miles").