The most common operation of handles or knobs on doors is by a simple spring assisted latch, more commonly known as a tubular latch. As the name suggests the spring operation is contained in a tubular case and fits into a 25mm hole drilled into the edge of the door.
Choosing Latches For Your Door Handles or Knobs
The most common size has a casing which is 63mm in depth and the distance to the middle of the square operating spindle is 44mm. This size of latch is used for the majority of lever handles on back plates, where the width of the back plate is about 40-45mm.
The next size of latch has a casing which is 75mm in depth and the distance to the middle of the square operating spindle is 57mm. A door latch this size is commonly used for levers on back plates where the width of the backplate is 50 to 55mm. This is the preferred latch for use with levers on roses, where the rose is generally 50mm in diameter. On some occasions you would use this size of latch for door knobs, but generally only ones up to 50mm in diameter.
Lock Cases
Less common are tubular latches which are 100mm, 125mm and 150mm in case depth. Used exclusively for knob sets, the choice of size is purely dependent upon the aesthetic appearance required on the door. It is important to remember that you need a certain amount of clearance to avoid brushing your knuckles on the door frame.
Latches also come in cases which are similar in size to lock cases. These are typically used in commercial applications or high quality domestic applications. For further details on the selection of these types of latches, please contact a member of our technical sales team
Door Latch Sizing
Here in the UK we have for many years had a standard size of 8mm for the square operating spindle in latches. Almost without exception, all lever handle sets sold today use or have a square spindle this size. Many years ago, before the introduction of decimalisation, the standard UK spindle was 5/16″ or 7.9mm. Not many of these latches are still in existence today and those that are will generally be in large horizontal 125mm and 150mm lock cases.