What type of file do you guys use to file down the front sights??

I have a buckhorn sight with a white ivory front sight. But it is not a bead. Is is similar to a traditional front sight. But it is actually a piece of brass folded in two with a tiny piece of ivory placed between the folds, then put into the front sight. It is actually very easy to use in the field. And the ivory shows up very well.

I used a piece of sandpaper to remove material from the ivory when I sighted those sights in. Tom.