Uni-ball Alpha-Gel Ballpoint Pen Black Ink Refills, 0.7mm, SA-7CN, Set of 3 (Japan import) Refill for Uni-ball Alpha-Gel Ballpoint Pen SD-507GG1P, Uni-ball Alpha-Gel Ballpoint Pen SD-617GG1P, and Uni-ball Laknock Retract Ballpoint Pen SN-100-07 . Ink color: Black The diameter of a ball: 0.7 mm. Medium type.