Some cards were not designed to be punched. These card may have been used as a header to provide an operator with context or instructions on a stack of cards or to separate sets of punched cards (these were often different coloured to stand out easily in a stack. Due to the standardised and ubiquitous nature of the 80-column punch card format and the availability of filing systems for these cards some organisations used index cards with identical dimensions to punched cards, often even using punched card paper stock.