I bought some Infini glass files from MicroMark a while ago, based on a recommendation from a YouTuber who is building a Tamiya F-4B, and used them for the first time today. I have to say that they are the best thing ever invented for cleaning up sprue attachment points. I use the Super Fine file (they come in a set of 3: medium, fine, and super fine) on attachment points and it not only makes quick work of removing just the right amount of material, but leaves a finely polished finish behind. The other great thing about these when cleaning attachment points on smaller pieces, is that they're a whole lot safer around your fingertips than that #11 blade is that a lot of us usually use for that task. They're all made of tempered glass, and have the abrasive surface permanently bonded to them. You can see right through them when filing, so its really easy to know when you're done. No more over-sanding and screwing up the shape of the part. A little pricey, but well worth it.