At the turn of the 20th century, women’s style was all big hair and big hats. And to keep those big hats on that big hair, dames needed big hatpins—giant needles up to 12 inches long.
The hatpins, used for self defense, grew longer and longer until they were banned in 1910. To quote one politician, “if women care to wear carrots and roosters on their heads, that is a matter for their own concern, but when it comes to wearing swords they must be stopped.”
Another article on this subject can be found at the Smithsonian’s website, along with sources at the bottom for the curious.