Abstract: An indexing mechanism is provided to enable discrete angular displacement of a first body 10 relative to a second body 12. An intermediate body 22 is provided, and is rotatable relative to both the first and second bodies 10,12. Mutually engageable detent elements on the first and intermediate 10,22, and intermediate and second 22,12 bodies, provide indexing of the first body 10 relative to the intermediate body 22 and the intermediate body relative to the second body 12 respectively. The angular separations of adjacent indexed positions provided by the first and second sets of detent elements differ such that the first body 10 is indexable relative to the second body 12 in finer indexing increments than are provided by either the first or second detent elements individually.