D1 Pen Refills
D1 pens refills measure 67mm in length and approximately 2.3mm in diameter and they are the standard mini refills used in almost all compact pens and multi-function pens. In this section you can find a range of D1 refills from brands such as Monteverde and Kaweco in a range of colour choices.
If you have a refill that looks the same size and shape as the mini D1 refills but also has the addition of a plastic screw section on the end, then the screw section is usually part of the pen. This should just pull off to allow you to add a new D1 refill then screw it back in place.