Wm. K. Walthers, Inc. / PROTO 2000 HO Scale Diesel EMD F7A-B Set Powered with Sound and DCC Rock Island #123 and 123B All-new drive Helical gears for ultra-quiet and smooth running 14:1 gear ratio for easy multiple-unit operations Five-pole, skew-wound, high torque, high efficiency can motor Both A and B units powered