Registration pin
A registration pin is a device intended to hold a piece of film, paper or other material in place during photographic exposure, copying or drawing. Registration pins are used in offset printing and cartography, to accurately position the different films or plates for multi-color work. In traditional, hand-drawn animation, the registration pins are often called pegs, and are attached to a peg bar. Also, in traditional, hand-taped printed circuit board artwork, usually at two or four times actual size. Sometimes on a single transparent base, usually mylar, with Layer 1 being on the front and  Layer 2 being on the back, in red and green, respectively, for later "separation" into component parts using a process camera. Motion picture cameras and related applications. In motion picture cameras, the pin(s) hold the film immovable during exposure. In certain "professional" motion picture cameras and "step" printers, there may be "two" registration pins: one is called the "big pin" and it is employed for primary (axial and lateral) registration while the other one is called the "little pin" and it is employed for secondary (axial) registration. With the "big pin"/"little pin" concept, it is not required to employ side  pressure or other means to guide the film through the intermittent movement with "absolute" precision as the "big pin" is fully fitting in the perforation (the "little pin" "is not" fully fitting in width, but "is" fully fitting in height; this difference accommodates slight changes in the dimensions of the film media due to changes in relative humidity and possibly other factors such as media age). This system is employed primarily in high-end "professional" cameras in the West. In the East (the former Soviet Union and its former Satellites), a single registration pin, corresponding to the "big pin", is  employed along with side pressure. Additionally, Western "professional" cameras "always" employ Bell and Howell (BH) pins whereas Eastern "professional" cameras "generally" employ Kodak Standard (KS) pins, which standard was originally recommended by the Western standards organizations, but was soundly rejected by Western studios and camera equipment manufacturers. Western "professional" cameras provided to the East during World War II's Lend-Lease program were "generally" converted to KS pins by the receiving country. To further improve registration accuracy, the perforations which are utilized for registration are "never" used for film advancement (i.e., for pull-down). The above description applies to "professional  applications, which is generally taken to mean film gauges larger than 16mm (i.e., 35mm and 65/70mm). For 16mm, only, a modified strategy is generally" employed, at least for "step" printers which utilize 1R (single-row) perforations. The lower pin, the "big pin", will be fully fitting in the axial "and" lateral dimensions but the upper pin, the "little pin", will be fully fitting in the lateral dimension "only", for the same reason that the "professional's" "little pin" is fully fitting in the axial dimension "only". This, then, also accomplishes "absolute" precision, but within the context  of "sub-professional" film gauges. For practical reasons, the 1R 16mm "little pin" is usually spaced two perforations above the 16mm "big pin". Again for 16mm, only, certain cameras and "step" printers which utilize 2R (two-row) perforations may employ the same strategy as for "professional" applications, but 2R is seldom utilized except for certain high-speed photography and almost never for duplication or prints.