Underwater decoration
I went and did a count up of my spare props a third of them are brass and more than a few paired contra rotating ones. I categorize at or below 40mm as small of which there were 85 and large up to 60mm 60 odd then there are about 20 boats so rarely short of a prop.
I do use them for testing the right prop to motor configuration for a new model. So not just sitting there.
regards
Roy