FUNCTION: The door hles have a small rotary knob on one side for internal door locking a safety release function on the other side. The door can be locked unlocked from the inside with a simple turn of a knob. They are used for interior doors to combine security privacy. DURABLE DESIGN: The sturdy construction of these door hles makes them strong, sturdy durable. The sturdy hle design prevents rattling breaking that can occur with inferior mortise door hles. The polished brass finish adds a touch of elegance to your home or office. SAFETY: These polished brass door knobs feature a safety feature on the exterior door knob. By using the supplied override key, the door can be unlocked quickly safely from the outside in an emergency. These security buttons are not designed for use with normal lock unlock keys. APPLICATION: These door locks can be used on interior doors with a thickness of 35mm to 45mm. The tubular latch is adjustable to 60mm or 70mm (the distance between the center of the hole the edge of the door). They are suitable for both commercial domestic applications.INSTALLATION: These chrome door hles come with fitting instructions templates for easy installation. All fixtures accessories are supplied with color matched screws, tubular latch override key. This set of knobs can be used for left or right doors.