First: Do NOT use corrugated cardboard to store ferris metal tools. Paper absorbs moisture and if you use it, your files will rust in a very short time.
Visit any Real Estate office and ask for an old sign. Realtors love having their signs printed on long-lasting corrugated plastic sheets and will eagerly let you have one for free. This plastic has larger, better formed corrugated openings than cardboard and will not damage your tools.
Plastic corrugation is perfect for storing needle files, mini screwdrivers, brushes or any other fine handled tool in your stable.