This is a toroidal propeller, which is quiter and more efficient than a traditional propeller. This model was created for an experimental submarine project but it may be used for other purposes. It is designed to fit a specific propeller shaft.

https://www.amazon.com/uxcell-Propeller-Universal-L130mm-Sleeve/dp/B07Q32MGV6/ref=sr_1_38?crid=GTA45A6JPKOD&keywords=rc+propeller+shaft&qid=1697407177&sprefix=rc+propeller+shaft%2Caps%2C107&sr=8-38

The Diameter of the Propeller is 120mm and has 4 “Fins”