9.5mm Collection

9.5 mm film is an amateur film format introduced by Pathé Frères in 1922 as part of the Pathé Baby amateur film system. It was conceived initially as an inexpensive format to provide copies of commercially-made films to home users, although a simple camera was released shortly afterwards.

It became very popular in Europe over the next few decades and is still used by a small number of enthusiasts today. Over 300,000 projectors were produced and sold mainly in France and England, and many commercial features were available in the format.

The format uses a single, central perforation (sprocket hole) between each pair of frames, as opposed to 8 mm film, which has perforations along one edge, and most other film formats, which have perforations on each side of the image. The single hole allowed more of the film to be used for the actual image, and in fact the image area is almost the same size as 16 mm film. The perforation in the film is invisible to viewers, as the intermittent shutter blanks off the light as the film is pulled through the gate to the next frame.
The width of 9.5 mm was chosen because three strips of film could be made from one strip of 35 mm film. This was useful when duplicating films, because only one strip of 35 mm had to be processed. Then the sides, which contained the special narrow 35 mm sprocket holes, were cut off, the remaining film was cut into 3 strips, and the central sprocket holes added to each new strip. 

Information from Wikipedia