One set of prongs is color-coded red; the insertion holes of the red bitewing film holder connect into both of these prongs when taking bitewing radiographs.
The bitewing film holder would be oriented in the mouth so that the film-holding plane is located between the tongue and the lingual aspect of the teeth being imaged.
Kodak Ultra Speed dental film (EP21, size 2), held in bitewing film
holders (Hawes-Neos, Bioggio, Switzerland) were used in combination with an Espectro II 50 kV, 10 mA machine (Dabi Atlante, Ribeirao Preto, SP, Brazil).
The assistant orients the film so that the white side of the film faces the flat horizontal plane of the bitewing film holder.
Technically, this bitewing XCP assemblage is incorrect, but it may result in acceptable bitewing films.