These are black 110v receptacle replacements mainly used for wall sconces that have an addition socket. These can also be used for a wall, but will require a special bracket for mounting. Face of outlet measures 1-1/8" x 1/2" and portion that would slide into a rectangular opening in a wall sconce measures 15/16" x 7/16". They have spring loaded wire clips to hold the receptacle into the holder.
Snap-in Convenience Outlet w/female terminal, has two 6" leads and accepts polarized plugs. Made to fit 1/2 " X 1" rectangular opening. 15A-125V.