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I present my pen refill adapter, for use in pens that take the Mont Blanc type Rollerball refill. It allows such pens to use the Mini/Multi D1 refills instead (not included). The Mont Blanc Rollerball refill is around 112mm long and 6.3mm in diameter. The D1 refill is around 67mm long and 2.3mm in diameter.
I appreciate that the D1 refill is generally a less practical refill, compared to the Mont Blanc Rollerball refill, in terms of ink volume. However, since the Mont Blanc refill is a propriatary refill (although Monteverde do make a compatible pattern refill), the D1 refills come in many more varieties, like the Pilot Hi-Tec-C Slims or Zebra JSB, which are not available in the Mont Blanc Rollerball refill size, so this adapter exists to hopefully provide flexibility, between your favourite pens and refills.
The adapter needs to be printed in the Frosted Detail material, as it's ability to hold fine detail is functionally desirable. The D1 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.
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.