What object pricks Aurora's finger and causes the curse?

The object that pricks Aurora's finger and causes the curse is a spinning wheel. More precisely, her finger touches the spindle of a spinning wheel, fulfilling Maleficent's prophecy on Aurora's sixteenth birthday.

Maleficent originally declares that Aurora will die before sunset after pricking her finger on the spindle. Merryweather cannot erase the curse, but she changes its outcome: Aurora will fall into an enchanted sleep instead of dying, and true love's kiss can awaken her.

King Stefan orders every spinning wheel in the kingdom destroyed, but Maleficent conjures one in a tower room. She hypnotically lures Aurora toward it, transforming the magical apparition into the wheel that fulfills the prophecy.

A common mix-up is calling the object a needle or simply a wheel. The dangerous part is specifically the spindle, while the full object is the spinning wheel. The 1959 film draws this episode from the older Sleeping Beauty tradition, including Charles Perrault's 1697 version.