Sash Locks — The Workhorse of Mortice DIN Locks
- FDH Team
- Sep 10
- 3 min read
What is a sash lock?
A sash lock is the most common type of mortice lock you’ll come across. It combines two functions in a single lock case:
A latchbolt, operated by a handle (keeps the door closed without locking).
A deadbolt, operated by a key or cylinder (engages securely into the frame).
This dual action makes sash locks versatile, practical, and the go-to choice for many fire doors in the UK. Unlike a simple latch or deadlock, the sash lock gives you everyday usability and added security in one package.
Anatomy of a sash lock
A DIN sash lock has a consistent case size and layout, making it easier to fit and replace. Key parts include:
Forend — the visible faceplate on the door edge.
Backset — distance from door edge to handle spindle.
Centres — distance from handle spindle to cylinder or keyhole.
Follower — square hole for the spindle bar that connects to handles.
Latchbolt — spring-loaded bolt retracted by the handle.
Deadbolt — solid bolt engaged by the cylinder or key.
Keeper (strike plate) — fixed to the frame, where latch and bolt engage.
👉 Not sure about any of these terms? Check our Door Dictionary.
Why sash locks dominate in fire doors
Standardisation — DIN dimensions (e.g., 72mm centres) mean consistency across manufacturers.
Fire compatibility — Many sash locks are tested and certified to FD30/FD60 when installed with intumescent lock kits and rated keepers.
Security + convenience — Everyday latch for normal use, secure deadbolt for locking, all in one prep.
Reduced cutting — One mortice instead of separate cutouts, maintaining door integrity.
Key dimensions you need to know
Before ordering or fitting, always confirm the following:
Backset: typically 55mm or 60mm for fire doors.
Centres: usually 72mm in DIN locks (critical for handle/cylinder alignment).
Case depth: how far the lock sits inside the door (commonly 85–100mm).
Forend size: the visible plate on the door edge, usually 235mm × 24mm for DIN.
Keeper type: ensure it’s tested and supplied with fire certification.
👉 To check your own measurements, use our Sash Lock & Keeper Calculator.
Choosing the right sash lock
Consider the following when specifying or replacing a sash lock:
Application: residential, commercial, healthcare, education.
Fire rating: FD30 or FD60 certification required.
Security: BS EN 12209 grade compliance if security is critical.
Material/finish: stainless steel for durability; brass or chrome for aesthetics.
Cylinder options: euro profile cylinder (master key, keyed alike, thumbturn).
Common mistakes to avoid
Fitting non-fire rated locks or keepers into certified door sets.
Mis-measuring the backset or centres, leading to poor handle fit.
Skipping intumescent lock case liners or pads in fire doors.
Mixing DIN and non-DIN prep across a project, creating fitting nightmares.
Sash lock vs other DIN mortice locks
Sash Lock → latch + deadbolt, handle + cylinder operation.
Deadlock → deadbolt only, no handle, pure security.
Latch → latch only, no deadbolt, used for passage doors.
Bathroom Lock → latch + privacy bolt, operated by thumbturn or cylinder.
👉 See our Mortice DIN Locks Guide for a full comparison.
FAQs
Do sash locks always need a cylinder?
Yes — the deadbolt function requires either a euro cylinder or key.
Are DIN sash locks reversible?
Yes — the latchbolt can be reversed for left- or right-hand doors.
Can I fit any sash lock to a fire door?
No — only locks with test evidence and certification can be used. Always check the door’s data sheet.
Summary
The sash lock is the workhorse of mortice DIN locks — reliable, versatile, and almost always the first choice when both latching and locking are required. For fire doors, it’s a proven solution when used with certified keepers, intumescent protection, and correct installation.
👉 Next step: Try our Sash Lock & Keeper Calculator to check your dimensions.
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