There is a Wikipedia page for the binder clip. It also is discussed by Henry Petroski (February 6, 1942 to June 14, 2023) in his last, 2022 book titled Force: What it means to push and pull, slip and grip, start and stop. He was a professor of both civil engineering and history at Duke University. In Chapter 12, titled Stretching and Squeezing (about springs) on pages 151 to 153 he says:
“Large lessons lie in small things. No matter what shape a paper clip may take, it is essentially a spring. The so-called binder clip keeps together sheaves of paper that are too thick for a regular bent-wire clip; the clever device was invented by a Washington, D.C., teenager named Louis E. Baltzley, who came from a family of inventors. His grandfather was Elias Howe, who is remembered for the sewing machine; his father and uncle also held patents. Young Louis, who would go on to invent small items including an easily picked up and stacked poker chip, a sifter top for powder containers, and a drinking glass holder for the side of a game table, wished to help his father, whose main occupation was writing, keep his manuscripts in order.
The binder gadget was patented in 1915 under the title ‘paper-binding clip,’ and throughout the subsequent century its appearance changed hardly at all from that shown in the drawings for Baltzley’s patent, attesting to the difficulty of improving upon it. Its basic element is a strip of spring steel formed into a shape resembling a pup tent. Two steel-wire handles bent into a keyhole shape fold over the tent sides to serve as levers by which to spread the top of the tent open wide enough to receive a sheaf of papers. When the handles are released on the spring-steel tent, which wants to assume its naturally closed configuration, it clamps down on the papers so firmly that they do not easily slip out.
Squeezing the shapely lever-handles of a binder clip between the thumb and index finger provides a strong sensation of the springiness. It is easy to open up at little gap but increasingly difficult to open up a wider one, just as Hooke’s law predicts. The clever design of the bent-wire handles enables the fingers to maintain their grip as they press with increasing force, which the user cannot help but feel. It is an ingenious device, and using it is an excellent way to feel the strong force of resistance that can come from even a small and compact device that looks nothing like a coil spring or the iconic Gem paper clip. It is also wonderfully adaptive. The handle loops allow the tightly clasped group of paper to be hung on a hook for ready access. When the handles are folded over onto the papers, they are out of the way for less visible storage. Alternately, the handles, which themselves are springs, can be manipulated to be removed entirely from the clip proper by squeezing their legs together sideways, and angling them out of the cleverly formed cylindrical recesses into which the edges of the clip terminate. By thus removing the handles from the clip or clips holding a set of papers together, a virtually permanent binding in book form can be achieved, with the backs of the clips forming a spine of sorts. In fact, a label could be affixed to the nearly flat back of a clip to identify what it holds.”
There is a broader discussion by Richard H. Moyer and Susan A. Everett in an article from EVERYDAY ENGINEERING on December 2011 (pages 16 to 21) titled Clips and Clamps.
An image of a binder clip holding a sheaf of papers was modified from Figure 3 of the patent 1,139,627.
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