On the back, beneath the engraving, there is a small button that is pressed in together with the new refill; this allows the click button together with the mechanism to be removed upwards and the old refill pulled out. The new refill must necessarily be fitted with an extension adapter, otherwise it does not fit. The usual Montblanc Ball Pen Refill is used, provided the adapter is present. If no adapter is left in the pen, it must be obtained separately.