A Stampede string is a long string usually made from leather

Leather

Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...

 or horsehair

Haircloth

Haircloth is a stiff, unsupple fabric typically made from horsehair and/or from the wooly hair of a camel. Although horsehair generally refers to the hair of a horse's mane or tail, haircloth itself is sometimes called horsehair...

. Typically, the string is run half-way around the crown of a cowboy hat

Stetson

Stetsons are the brand of hat manufactured by the John B. Stetson Company of St. Joseph, Missouri.Stetson eventually became the world’s largest hat maker, producing over 3.3 million hats a year in a factory spread over . Today Stetson remains a family-owned concern...

, and then through a hole on each side with its ends knotted and then secured under the chin or around the back of the head keeping the hat in place in windy conditions or when riding a horse.