Mortise Locks & Ironmongery Terminology

You may remember the post where I finally decided on what door handles to go with for our study and bathroom door.

What I hadn’t anticipated was that when I ordered them they would literally JUST come with the handles, and none of the other door ironmongery components. Argh! At work we typically work with an ironmongery rep who helps us with the specification for all the other components that you don’t see, but this time with my order of 2, I was on my own.

To complete my order, I had to quickly get familiar with the more detailed world of ironmongery specification.  My idea of simply going online to SDS Ironmongery to buy a bathroom mortise lock didn’t turn out to be so simple. There were 16 different types bathroom mortise locks. Which one did I need?  One with a heavy or light spring? An 8mm or 5mm ‘Follower’?  What size case did I need? and should I get the DIN one?

Here are a few things I learned from the knowledgeable people at SDS: (apologies in advance for the somewhat technical nature of this post, I just wanted to get this information down for future reference!)

  • Door handles from Europe typically come with a 6-8mm spindle or ‘follower’, while in the UK they are 5mm. (This means I need an 8mm spindle for my Danish DLine handles as they only come in two sizes – 5mm or 8mm)
  • If the spindle is less than 8mm, a spindle adaptor can be added to thicken it up to suit the mortise
  • Lever handles are typically sprung, so only require a light spring (It turns out however that my DLine lever handles are not sprung at all so would need a double sprung mortise lock)
  • Door knobs are typically not sprung, and so require a heavy spring
  • If you don’t use the right strength spring, the lever handle will droop and not spring back after a few weeks
  • The backset is the distance that the knob is positioned from the edge of the door
  • The larger the mortise case dimension, the larger the backset distance
  • Door knobs need to be set farther away from the edge with a larger backset distance (say 101mm) so you don’t bump your knuckles on the door architrave
  • Lever handles can have a shorter backset (76 or 64mm) as your hand is positioned farther from the door edge when operating the handle
  • You should also check the vertical distance between the follower (spindle) holes to make sure that the rose on your lock will not be too close to the rose on your door handle.
  • Strike plates are what the latch hits against on the architrave
  • Strike plates can have straight or ‘radius forends’ – this is the shape at the end of the metal plate.
  • the DIN range is typically specified on public buildings and large scale projects where you want all the cases to be the same, regardless of whether it latches or not so that all doors can be pre-cut with the same hole. ie you don’t need this on a residential project.

In the end, I had to go back to DLine as SDS didn’t sell an 8mm follower, double sprung mortise lock case. The mortise case DLine advised was suitable has a radius forend, which I quite like as it matches the oval privacy latch, and 78mm separation between fixing holes.

More about locks here.


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