Useless fact
What is the metal piece at the bottom of a zipper?
The small metal or plastic box at the bottom of a jacket zipper that receives the pin to start the zip is called the retainer box.
The modern zipper evolved through several stages, but the separable zipper—commonly used on jackets to allow the two sides to detach completely—requires a precise starting mechanism. This mechanism consists of two main parts at the bottom: a pin on one side and a receiving box on the other. Officially called the retainer box, this tiny metal or plastic component aligns and holds the insertion pin, allowing the slider to run smoothly up the tracks. The development of this separable end was a major breakthrough in fastener technology, patented by Swedish-American electrical engineer Gideon Sundback in the early twentieth century. Before the invention of the retainer box and pin, zippers could only be used on openings that remained closed at one end, such as trousers or bags. Today, major global manufacturers like YKK standardize this terminology, ensuring consistent specifications across the fashion and textile industries.
Why this is true — The official term used by major manufacturers like YKK for the receiving component of a separating zipper is the retainer box.
Sources
- Structure of a Zipper YKK Corporation
- Separable fastener United States Patent and Trademark Office