F3A Propellers

Factory recommended combinations of contra rotation propellers
20.5×20.5 (Front) 20×22.5 (Rear)
  21×20 (Front) 21×20 (Rear)
22×16.5 (Front) 22×18.3 (Rear) 
  22×18 (Front) 22×20 (Rear)
22×20 (Front) 22×22 (Rear)
  22×22 (Front) 22×22 (Rear)
22×18 (Front) 22×18 (Rear)
  23×18 (Front) 23×20 (Rear)
23×20 (Front) 23×22 (Rear)