SAFCO (Mayline) straightedges are perfect for engineering and construction applications. Every Mayline parallel ruling straightedge begins with a durable, black phenolic laminate base with a transparent blade for see-through registration and fine line quality. For those who work with a variety of surfaces, this straitedge is designed with retractile, ball-bearing rollers of metal or Delrin (plastic) built right into its base. They literally float over any surface whether it's paper or film. Above-board mounting hardware included. Made in the USA. FREE GROUND SHIPPING TO 48 LOWER US STATES.