Wow! You are Lucky.
Monteverde rollerball pens fit our #1 selling refill. The Monteverde brand features the R4688 which offers three different points sizes (rare in the rollerball world). This refill was specifically designed to replace the Schmidt 888 found in many rollerball pens.
The Monteverde Spring Loaded Fineliner offers a "felt tip" point and the Monteverde Wide Writer which features medium and broads and fits especially well in Pelikan rollerball pens. All of these refills fit perfectly into your Monteverde rollerball pen. Your choice is primarily one of rollerball or Spring Loaded Fineliner, colors, point sizes, brand and price.
If you are an owner and fan of the Monteverde Engage rollerball pen which uses a fountain pen ink cartridge instead of a rollerball refill, then you know that the tips of these economical pens need to be replaced periodically. You'll see an option for those, so stock up!
And remember, when you buy refills from Colorado Pen, you are buying from the single largest seller of refills in North America. We have the freshest inventory outside of the factories themselves. Every refill we ship is unconditionally guaranteed to write as described or we'll replace it at your request. Never any questions asked.