Mortice DIN Locks (What They Are, How They Differ, and How to Specify Them)

Sash | Latch | Bathroom | Deadlock

1) Quick intro: what “DIN” actually means

“DIN” is short for Deutsches Institut für Normung — the German Institute for Standardization. In door hardware, “DIN-style” mortice locks follow German/European dimensional standards that make hardware highly interchangeable and easy to specify.

Across UK commercial and fire doors, DIN-style Euro-profile mortice locks are widely used because they share consistent geometry (notably the centres dimension), so handles/escutcheons/cylinders from different brands will fit the same cut-outs.

The headline dimensions you’ll see again and again

• Centres (PZ) – distance from spindle (handle) to cylinder: 72 mm is the DIN standard for Euro-profile locks. (Bathroom privacy versions typically use 78 mm.)

  
  

• Back-set – distance from door edge to spindle/cylinder: typically 55/60/65 mm (DIN ranges vary by manufacturer).

  
  

• Follower – square hole for the lever handle spindle: 8 mm (DIN standard).

2) What a “mortice” lock is (and how it differs from a rim lock)

A mortice lock is fitted inside the door leaf, in a pocket (“mortise/mortice”) cut into the edge of the door. It’s the opposite of a rim lock, which is surface-mounted on the face. Mortice construction gives better security, a cleaner look, and compatibility with modern Euro cylinders and lever furniture.

3) The main DIN mortice lock types you’ll meet

Each lock type is shown with its typical centres/back-set and the keeper (strike) you’ll use in the frame.

A) Sash lock (latch + deadbolt) — the workhorse

• Use case: General doors needing a handle to latch and a key/thumbturn to deadlock.

  
  

• Geometry: Centres 72 mm; common back-sets 55/60/65 mm; 8 mm follower.

  
  

• Keeper: Sash strike (accepts both latch and bolt). For fire doors, choose the manufacturer-approved boxed or reinforced keeper and add any specified intumescent.

When to pick it: Almost every day — offices, hotel rooms, classrooms, plant rooms (with the right cylinder/turn & function).

B) Bathroom/WC (privacy) lock

• Use case: Toilets, shower rooms, changing rooms; requires a turn & emergency release rather than a key.

  
  

• Geometry: Centres 78 mm (handle to turn); typical DIN back-sets as above; 8 mm follower.

  
  

• Keeper: Bathroom strike (for the latch and privacy bolt), again using the maker’s approved version for FD30/FD60 and intumescent as specified.

  
  

Remember: On escape routes, avoid any lock that could delay egress — use the correct emergency or panic hardware standard (EN 179/EN 1125) where required.

C) Deadlock (bolt only)

• Use case: Secondary security (e.g., storerooms) or combined with separate latches/closers.

  
  

• Geometry: Usually retains the DIN 72 mm relationship to cylinder position; common back-sets 55/60/65 mm.

  
  

• Keeper: Box keep for the deadbolt; choose the tested keeper per the door leaf’s fire certification.

  
  

Pro tip: Deadlocks on final exits/escape routes must not compromise evacuation — check function and local fire strategy.

D) Latch (latch only)

• Use case: Non-locking passage doors (office corridors, cupboards) where a lever handle simply pulls the latch.

  
  

• Geometry: Same DIN body family; no cylinder; 8 mm follower.

  
  

• Keeper: Latch strike (shallow). For fire doors use the keeper/intumescent set from the lock’s fire assessment.

4) Anatomy & terms you’ll specify (fast)

• Centres (PZ): 72 mm for Euro cylinder locks (DIN); 78 mm typical on bathroom/WC versions.

  
  

• Backset: 55/60/65 mm (check the door stile width and any glass/bead lines).

  
  

• Follower size: 8 mm square spindle (lever handles).

  
  

• Forend/Strike style: Square or radius; flat strike vs box strike; timber vs metal frames (manufacturer usually offers both).

  
  

• Handing: Most DIN locks have reversible latches; check if the bolt is double-throw or requires handing during install (maker’s sheet).

5) Fire door essentials (don’t skip)

1. Choose the right standard/classification

   
   

   Mechanical locks & latches are classified to EN 12209 / BS EN 12209; always select a lock that is fire-suitable in that standard and also fire-tested on the actual door type to EN 1634-1 (or the door manufacturer’s own test report/assessment).

   
   

2. Fit the intumescent kit exactly as tested

   
   

   Many locks require intumescent lock protection (wraps/liners) around the case and sometimes behind the strike to maintain the FD rating (e.g., FD30/FD60). Use the lock-specific or door-leaf-specific kit and thickness.

   
   

3. Through-bolting & fixings

   
   

   On heavier doors/closers, through-bolt lever furniture where specified (often required for EN 1906-rated handles) to avoid pull-out in fire.

   
   

4. Cylinders & turns

   
   

   For Euro cylinders, pick an EN 1303-classified cylinder appropriate to the risk, and select thumbturns on escape routes for keyless egress where the fire strategy demands it.

   
   

5. Certification first, always

   
   

   Your door leaf & frame certificate rules the job. Use only the lock/furniture/closer/hinges (and intumescent pack) listed for that door set, in the exact prep and position.

   
   
   
   

6) Choosing the right keeper (strike) for the frame

• Timber frames: use the lock maker’s flat or box strike as specified; many FD doors require a boxed keeper for bolt engagement.

  
  

• Steel frames: use the dedicated steel frame strike; tolerances/gap backing plates differ.

  
  

• Rebated meeting stiles (pairs): use the manufacturer’s rebate kit version of the lock and strike.

7) Why DIN locks simplify your life

• Interchangeable geometry – 72 mm centres and common backsets mean furniture and cylinders are swappable across brands.

  
  

• Consistent spindle – 8 mm follower standardises lever compatibility.

  
  

• Clear families – Sash, bathroom (78 mm), deadlock, latch; most come in the same case envelope for simple door preps.

8) Spec checklist you can copy/paste into a job sheet

• Lock type: Sash / Bathroom (78 mm) / Deadlock / Latch

  
  

• Standard & fire: EN 12209 classification fire suitable + door leaf EN 1634-1 evidence

  
  

• Centres (PZ): 72 mm (Euro); 78 mm (bathroom)

  
  

• Backset: 55 / 60 / 65 mm (match stile width)

  
  

• Follower: 8 mm

  
  

• Forend/Strike: Square or radius; flat or box; timber or steel frame variant

  
  

• Intumescent kit: Part no. / thickness per certificate

  
  

• Cylinder: EN 1303 grade; length to suit door & escutcheons; thumbturn if required

  
  

• Furniture: EN 1906 grade; through-bolted if specified

  
  

• Handing: Reversible latch confirmed / handed bolt if applicable

9) Common pitfalls (and how to avoid them)

• Wrong centres/backset → furniture/cylinder won’t line up. Confirm 72 mm (or 78 mm WC) and backset before cutting.

  
  

• No intumescent → certification fails. Order the correct kit with the lock.

  
  

• Using a non-fire-rated keeper → bolt engagement may fail under heat. Use the tested strike from the same system.

  
  

• Cylinder too long/short → security/appearance issues. Measure door + furniture thickness and select the correct split length.

  
  

• Wrong function on escape route → consult the fire strategy and EN 179/EN 1125 requirements early.