One of the many small clamp on parts made by Camapgnolo to attach your frame pump to the bicycle.
This one ends in a rounded clip that the end of your frame pump seated completely into.  It is sometines called the "Umbrella" pump clip as its shape is reminiscent of an umbrella.

This was the the style of pump clip typically used with Silca Impero non-frame fit pumps and the like.
This part was redesigned slightly in 78 for the C.P.S.C. (Consumer Product Safety Commission).