Years ago on a 190SL, I painted the hubcaps by manually masking the star and outer chrome portion (if that's what you're attempting). To do this, you use sufficient masking tape to cover the star (and of course some of the area of the hub cap center that you want to paint), then use an Exacto knife (pencil sized razor knife) to trace around the star. Once you have traced all around the star, you use the edge of the Exacto to lift the tape that you want removed, leaving a nicely masked star. Easy to do and it works very well.