That refers to the difference in gearcases on the 2 cylinder 45 HP , yes 45 hp outboards.-----The 2 cylinder 40 / 45 / 48 / 50 / 60 HP gearcases are not known to be robust !!----Therefor the 3 cylinder 70 HP was adapted for them.-----The little 6 / 7.5 / 8 HP motor does not need the " monster...