Both handlebars are made by Nitto in Japan, but in collaboration with different companies. The B903aa bars are designed by Fairweather, and the B904aa is designed by Rivendell. Lets see the difference.....

Similarities are - 

• CrMo steel 
• Single pinch bolt design for 1-1/8"
• Both are available in silver

Differences are - 

• Extension
• Width 
• Sweep
• Rise
• B903 available in black