The standard factory prop for the 25 horse RD-Big Twin was/is 10 3/8" by 12 1/2" – the 35 was 10 3/8′ by 13 1/4" and the 40 was 10 3/8" by 14". Michigan Wheel made a 10 1/2" by 11" for barges and deck boats. There was also a four bladed Michigan Wheel that was 10 1/2" by 10". . . 😎
