A single knob cylinder is a type of lock that is used to secure doors or windows. It consists of one cylinder that is installed on one side of the door or window, so that the door or window can only be opened from one side with a key or with a knob. Single knob cylinders are often made of steel or brass and are designed to be strong and durable. They are often used on doors that are accessible from the outside, such as exterior doors, to prevent someone from unwantedly opening the door without a key. Single knob cylinders can also be used on windows that are accessible from the outside, such as ground floor windows or windows that are easily accessible from the outdoors. Single knob cylinders provide security against break-ins and can help make your home or building safer.