They resemble a U-reversed and are clutches for wheel hubs. In the last few years, they have a security lock “inherited” from mountain bikes. In the road bicycle, however, the locking function is useless because a narrow wheel will not loosen with the vibrations of the road.
Sources:
http://www.cyclinside.it/web/category/componenti/
http://www.albanesi.it/corsa/ciclismo.htm