Perfect for engineering and construction applications.  Every Mayline straightedge begins with a durable, black phenolic laminate base inset with a transparent blade for see-through registration and fine line quality.  For those who work with a variety of surfaces, we designed a straightedge with retractile, ball-bearing rollers of metal or delrin built right into its base.  They literally float over any surface wheather it's paper or film.  The rollers come in chrome-plated brass or plastic.  We reccommend the plastic rollers for use with drafting films.  Above-board mounting hardware included.