Pentel EnerGel refill, 0.5mm. I'm selling these because I no longer use them. Two red and two blue refills are unopened. There is also one each of red, blue, and black refills that have been used. Please check the remaining ink levels in the photos. I have tested the used refills and confirmed they work, but I have not checked the unopened ones. They were purchased about 1-2 years ago. Please understand that these have been stored at home. If you have any questions, please ask before purchasing.