The lint sheets are 4 by 6. I use scissors to cut the size I need or just use the whole sheet. The individual sheets are perforated (very finely) so you can use any length you desire but you're limited by the 4-inch width. Sheet tack extends right to the edge so you can butt ends.
I then take the sheet and attach it to the part to be painted and lightly pencil the areas to be cut out. You don't have to stick the sheet down to the part with any great force because it's very tacky.
I then pull the sheet off the part, put it on a piece of glass and use a exacto knife to cut out the part