Engineers Scale 4 Bevel Flat 6" 311E Model Plastic Known as an Engineering Rule or Ruler Graduations Include: 10, 30, 40, 50 parts per inch. Four Bevel Flat Scales - high quality architects scales and engineers scale by Alvin. Perfect for Architectural & Engineering design the 260 series Alvin four-bevel scales are made of high impact white plastic. These scales are available in 6 inch and 12 inch lengths with printed graduations. Supplied in vinyl sheath.