It came up in a different context, so thought I would post :-) If you trim a tiny smidge from the butt end of a uni-ball Signo 207 refill it fits very nicely into the Pilot G2 Pro body. The G2 Pro body is my favorite everyday pen body, but the G2 cartridges (what do you call them when they include the ball, anyway?) tend to be uneven and even blotchy on me compared to the 207s. So, a couple seconds with a pocketknife and I have the best of both worlds!