I dont really believe the prop is 53.5cm or 21 inches long. Descriptions always round up or down. In that same post you can see the image where the hilt is longer than 21.5 inches
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Here is another prop that is clearly more than 21 inches long (almost 22). It starts at about 4.25 and ends about 26" so its like ~21.75"
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Sorry, i don't believe its smaller (shorter).
Regarding the diameter, I dont have the actual prop to measure it but using the above image I estimated it was close to 35mm. I wouln't dare use any other makers size as reference, even if they had an actual prop. So all i have is those images.
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The prop image i used for reference is a cleaner cast which leads me to believe it's an earlier cast from the master, and as you know resin shrinks.
Not saying mine is the correct one, just saying how i came about the 35mm diameter. I have used this technique with all the clans I've made.