The numbers go 6 1/8 inches in diameter by 6 1/4 inches of forward travel in one rev. Michigan Wheel is a company that makes props, they used to have their own part numbers for props they made to fit different motors. Google prop 203919 and see where it takes you. Call michigan wheel, they may have new old stock of your prop. That prop was used for at least a thousand years, so somebody, somewhere has got one. This site had them last year, I was looking for the prop ring and I saw that they had the prop too. So, it's only been unavalible for less than a year. If all else fails try ebay.