Abstract: A refill unit (1) for a writing instrument has a writing tip (5) at one end and a ratchet mechanism (7) at the other end through the use of which the unit (1) can be turned and selectively extended from and retracted into the writing instrument. The ratchet mechanism (7) is rotatable about the longitudinal axis of the unit with respect to the writing tip (5). Each time the refill unit (1) is extended from or retracted into the writing instrument, the tip (5) rotates by a substantially random amount which ensures a more even distribution of wear on the writing tip (5).