Kids made fidget spinners wildly popular. Now, adults are keeping them that way.

The spinners, hand-sized toys balanced with ceramic ball bearings weighted in the center and three rings on the outside, stay in motion between one's fingertips with little effort. The toys sell for $7 to $20.

Fidget spinners were invented in the 1990s in one of two ways, depending on which story one reads. Both stories credit Catherine Hettinger of Florida as the inventor.

One claims Hettinger heard about boys throwing rocks at police officers and wanted to give them something to do. The New York Times interviewed Hettinger and said she created the toy after her myasthenia gravis, an autoimmune disorder that causes muscle weakness, made her unable to play with her elementary school daughter.

Hasbro initially passed on the toy in the 1990s. But it eventually got marketed, and this year it took off. There's enough hoopla that fidget spinners have been declared the new hula hoop. Or Slinky. Or yo-yo. You get the idea.

Amazon, which listed fidget spinners in each of its top 20 bestselling toy spots in May, features at least one fidget spinner geared directly to adults: the "HITASION Hand Spinner Fidget Toys for Adults," a high-speed spinner that costs $9.77.

The spinners have been touted as a remedy for students who have trouble focusing or paying attention. Adults might be using them for similar reasons but keep their use under the table — including the conference table.

Aubrey Scheopner Torres, assistant professor of education at St. Anselm College in New Hampshire, looks at fidget spinners from the perspective of an educator — and a spouse. Her husband owns three. The fidget spinner helps him focus, she said. He's the type of person who "has five TVs on at one time."

You can have a stress ball in the office, she said. But with fidget spinners, "you can literally put [them] in a pocket and take anywhere you go."

For those with anxiety, fidget spinners help release some of the tension.

The first time Mario Sinclair, education assistant for special education at Milwaukee College Prep, saw a fidget spinner it was in a classroom. Now he has one of his own to "regulate personal energy."

Jay Tarbah finds his fidget toy useful when he's on the phone or watching television. He uses his any time he would ordinarily find himself scrolling online.

"Used to be I would watch television and I'd also be on my phone," said Tarbah, who has a fidget cube, a cube-shaped version that lights up or makes noises.

The 31-year-old didn't expect to make the purchase. He walked into a toy store to buy a gift for his nephew. He walked out with a fidget cube for himself.

Marianne Szymanski, who founded Milwaukee-based Toy Tips, which provides parents with information on toys that build skills and enhance a child's personal development, considers fidget spinners "sensory stimulation" and a mindless toy that can calm through its constant motion.

Scheopner Torres thinks the popularity of the toys caught schools off guard this year. The same thing that can calm one student becomes a distraction to others. But it's likely fidget spinners for children have peaked to be replaced by summer activities. Now it's just their parents who are fascinated with them.