The most common operation of any door handles or door knobs is assisted by a simple spring latch, more commonly known as a tubular mortice latch. As the name suggests the spring operation is contained in a tubular case and fits into a 25mm diameter hole drilled into the edge of the door.
Choosing Latches for your Door Handles or Knobs
Backset-size: It is important to choose the correct backset size of the latch since you need a certain amount of clearance to avoid brushing your knuckles on the door frame.
The most common size has a casing which is 64mm in depth and the distance to the middle of the square operating spindle is 44mm. This size of latch is used for most lever handles on back plates, where the width of the back plate is about 40-45mm.
The next common size of latch has a casing which is 76mm in depth and the distance to the middle of the square operating spindle is 57mm. This size door latch size is commonly used for lever handles on back plates where the width of the backplate is 50-55mm. This is the preferred latch for use with levers on roses or door knobs, where the rose is generally 50mm in diameter.
Less common sizes of tubular latches are 100mm, 125mm and 150mm in case depth. These are used exclusively for knob sets and the choice of size is purely dependent upon the aesthetic appearance required on the door.
The backset size must also be considered in the same manner when choosing the mortice sashlocks or bathroom locks for your home.
Hiatt Hardware offers tubular latch, sashlock and bathroom locks in 64mm and 76mm backsets.