Although it's called a "file" being "grit" it's really a coarse abrasive stick. Smooth draw filing is done with a mill file and can give a very smooth surface especially if followed with a scraper (one-tooth file).
There's another one that has a wire core too, you just wanna make sure you don't get fiber core like Ryan said.
Oh, me? I'm just a recovering blacksmith.
Pretty nice Geoff! Humbling (and rewarding) to hear that I might have inspired you. Looks like you did a first rate job. LOL, you don't want to look in my head either!