Alvin 304E engineers scale ruler is constructed of high-quality, solid aluminum. Printed calibrations on a durable, ultra-smooth surface that resists stains and abrasions. Color-coded furrows for quick and easy reference. 4" triangular scale with standard engineering graduations of 10, 20, 30, 40, 50, & 60 parts per inch. Compact size is great for travel and on-the-job use in the field.