Roller skating has been a beloved activity for both kids and adults across generations.

The first recorded use of roller skates dates back to 1743 in a London stage performance, with John Joseph Merlin claiming to have invented the first roller skate in 1760 while living in London.

Roller skates even made an appearance during World War II, when the U.S. considered using them to transport infantry across Europe to save fuel—a plan that never came to fruition.

In the U.S., roller skating became popular in 1935, and in the 1970s, skating rinks playing disco music made the activity even more trendy.

For those who remember, you might recall the heavy metal skates that attached to shoes and could be adjusted as your feet grew. But you may not recall a small metal object that many skaters wore around their necks.

This object, which has recently been shared on social media with many guessing it’s a bottle opener or some sort of tool, is actually a skate key. For those skating before the 1970s, it was a crucial piece of equipment.

The skate key was used to adjust the size of the skates, which would be strapped onto your shoes. It would fit into the back of the skates, and many skaters wore it around their necks to keep from losing it while skating.

In fact, songs have even been written about this essential tool for roller skaters.