I present my pen refill adapter, for use in pens that take the Lamy M22 type ballpoint refill. It allows such pens to use the Cross Matrix refills instead (not included).
The Lamy M22 refill is around 60mm long and 5.9mm in diameter. The Cross Matrix refill is around 36mm long and 2.3mm in diameter.
I appreciate that the Cross Matrix refill is generally a less practical refill, compared to the Lamy M22, in terms of ink volume. However, since the Lamy M22 is a propriatary refill, having the Cross Matrix refills as an alternative option has it's advantages, especially as some people find that the Lamy M22 refill doesn't give them a particularly good writing experience.
Also, the Cross Matrix refill is just a shorter version of the standard Mini/Multi D1 refill, which come in many more varieties. D1 refills could be cut down to take the place of the Cross Matrix refill, so this adapter exists to hopefully provide flexibility, between your favourite pens and refills.
The adapter needs to be printed in the polished white or coloured plastics, as the smooth polished finish is functionally desirable. The Cross Matrix refill is held in place, by the adapter, using friction. The holes around the side of the adapter are present to help with the removal of unbonded plastic powder from the core, when being polished. However, some powder may still need to be removed, with a pin or thin metal rod, before inserting the refill.
Due to the very varied nature of pen design, I cannot guarantee that this adapter will work with any specific pen, although I've made every effort to make it as universal as possible. The neck of the Lamy M22 refill is 2.2mm in diameter, while the Cross Matrix and D1 are 2.3mm in diameter. Some Lamy pens may have a hole at the pen tip which is too narrow for the Cross Matrix or D1 refill, without modification.
I plan to make as many refill types compatible with as many host pens as possible, so If you have any suggestions on refill adapters, please let me know and I can hopefully make it available, depending on the relative sizes involved. I have now created dimensioned drawings of over 80 standard and obscure ballpoint, gel and rollerball refill types, so I like to think that I have a fair idea of what is and isn't possible.