Single-8 is a motion picture film format introduced by Fujifilm of Japan in 1965 as an alternative to the Kodak Super 8 format.
Although the film is thinner, the other dimensions of Single-8 such as the sprocket holes and sound track, are the same as Super 8. Single-8 can be projected in Super 8 projectors and vice versa. Single-8 comes pre-loaded in B-shaped cartridges, with two separate spools unlike the coaxial system of Super 8. As a result, Single-8 film offered unlimited rewind, whereas Super 8 rewind was limited to several seconds and relied on there being sufficient empty space within the cartridge for the rewound film to pile up inside.
The Single 8 cartridge was designed to use the camera's film gate to hold the film in place during exposure. This contrasted with the Kodak system which had a plastic pressure plate built into the cartridge. It was widely believed by Single 8 enthusiasts that this would offer superior film positioning, but the reality was that Super 8's plastic pressure plate could be moulded with far smaller tolerance than Single 8's metal version could be machined.
RK100D Single-8 ISO/ASA 100 Daylight Color reversal film with processing