A string of prayer beads, most commonly used in the Catholic Church. A system of prayers is said on the beads as a devotion to the Virgin Mary.
When the demon Meg threatens to kill each and every one of John's friends, unless he hands over the Colt. Capitulating, John agrees to meet her in Lincoln at midnight for the trade. The boys protest handing the gun over, but John has a plan: they will use a substitute gun since Meg doesn't know what the real one looks like.
John arrives in Lincoln to meet Meg. He cases the area for escape routes and traps and finds a water tank to bless by dropping a rosary into it. When John confronts Meg, she is joined by a demon named Tom, John hands the gun to Meg and she in turn hands it off to Tom, asking if he thinks it’s the real thing. Without warning, he shoots Meg. When the demons realize the Colt is a fake, John runs and deters them by releasing a valve, thereby spraying them with the holy water he prepared earlier.
When Dean, Sam, Bobby and Ruby finally track down Lilith at the home of the Freemont family. Bobby blesses the sprinker system with a rosary, so when it turns on, it will block the house Lilith is in with a wall of holy water, preventing other demons from entering the home.