Perforation holes are responsible for the transport of film stock during its exposure, laboratory processing and screening. Setting the standard – 4 perforation holes on two sides of each frame of 35 mm film – lasted as long as until 1923. Initially, the size and shape of perforations was indicated by the manufacture that produced film materials. The holes could be rectangular, with rounded corners or entirely round.

Auguste and Louis Lumière films.
From: http://www.tcf.ua.edu/Classes/Jbutler/T112/EdisonIllustrations.htm

STANDARDISATION OF PERFORATION

In 1923, the company Kodak came up with the standard shape of perforation holes of 35 positive print (suitable for screening at the cinemas). The shape was known as Kodak Standard (KS) and (P). In turn, the perforation holes of 35 mm negative were designed by the company Bell&Howell. It was marked with the abbreviations of Bell&Howell (BH) and (N). Positive perforation holes were bigger and rounded. They provided for smooth transport of film stock inside the screening device and reduced the risk of tearing. Negative perforation (BH) was characterized by sharp corners, more precise, which contributed to the reduction of vibrations of film during exposure and copying the negative.

In the years 1934 – 1936, it was decided to merge the two types of perforation by proposing the standard Dubray-Howell (DH). However, the majority of manufacturers were not successfully convinced to introduce the uniform solution. Perforation holes of the same height as (BH) and the shape of (KS) came to be definitely rejected in the course of time.

The invention of CinemaScope in 1953 required the introduction of a new shape of perforation holes. Due to four magnetic soundtracks ensuring surround sound, perforation had to be decreased. This type of holes acquired the name CinemaScope (CS) and (S) or Fox Hole.