Abstract: A propeller according to the invention has a hub centered on and rotatable about a hub axis and formed with a bore extending along the axis and with a plurality of identical, radially outwardly open, and angularly equispaced sockets centered on socket axes extending at least generally radially of the hub axis. Respective identical blades each have a base complementary to and snugly fittable in the respective socket and an outer part extending radially outward from the hub along the respective socket axis when the respective base is fitted therein. Respective locks are provided in the hub for releasably fixing the bases in the respective sockets against relative movement between the respective blades and the hub. The sockets and bases are normally complementarily cylindrical and both centered when the bases are in the sockets on the respective socket axes. Thus the blades can turn about the respective socket axes on the hub when released by the respective locking means.