Bolt, Side or Centre: Choosing a Lock for Glass Sliding Doors

Locks are the last line on a glass sliding door quotation and the one most people skim. It is a fair reaction — you have just spent a considerable amount on a wall of frameless glass, and a small ironmongery item at the end feels like an afterthought. It is not, quite. Which lock you choose determines where you stand to close the doors, how much of the opening you lose, and whether the run is closed at one end or in the middle.

There are three sensible options on a Fiano system, they cost noticeably different amounts, and the right one depends less on security than on how you actually use the space. This is what each does, what it does not do, and — with apologies — what they realistically prevent.

The Three Options

The simplest is a profile bolt lock: a small surface-mounted housing with a key cylinder on the U profile at one end, with a pin that shoots sideways into the frame of the sliding panel. No handle, no mechanism running up the door, nothing else to look at.

Then there are two versions of the same handle-based closure. A side lock or centre lock is a full-height assembly: a handle profile bonded to one glass panel, a multi-point locking bar running its length, and a double-sided handle with a key cylinder on one face. The difference between the two is purely where it goes. A side lock closes the run against a wall, façade or post at one end. A centre lock closes two panels against each other in the middle of the opening.

All three come in the system colours — graphite grey, cream white, traffic white and black — and all three are made for the 10mm toughened glass these doors use.

The Bolt Lock

Cheap, unobtrusive, and rather better than its price suggests. The anodised profile bolt lock is a compact box on the U profile at one end of the run, and a 14mm pin that engages a hole drilled into the frame of the sliding panel.

The case for it is that it adds almost nothing visually. On a frameless system where the whole point is that you are looking at glass rather than at frames, a full-height handle assembly is a vertical line you have deliberately introduced. A bolt lock is a small housing at ankle height that you stop noticing within a week.

The case against is that there is no handle. You are pulling the panels by the edge of the glass and turning a key at floor level, which is fine when you are the one who bought it and less fine when it is your mother-in-law with a tray. It also secures one panel rather than pulling a run tight, so it is a closure rather than a clamp.

One detail from the manual is worth knowing because it explains why this is not a job to improvise: the pin must engage the lower half of the panel frame, below the glass. Fit it too high and the pin bears on the glass itself, and the glass loses. The hole is drilled to 12mm and deliberately not right through.

The Side Lock

The side lock is the version most people end up with, and it is closest to what you would expect from a door.

The handle profile fits to the outermost panel at one end, and a locking profile is fixed to the wall, façade or post it closes against. Inside runs an espagnolette — a multi-point bar with cams that engage along the height rather than at a single point — operated by a lever handle on both faces with a key cylinder on one. Turn the handle down and the whole panel is drawn tight against the locking profile.

What that buys you is a proper handle to grip, a positive closed position that pulls the panel in rather than merely restraining it, and a locking action along the full height. On a run that gets opened and closed daily, it feels like a door instead of a puzzle.

The costs are that it is a visible full-height profile on one panel, and that it takes space. When you specify a side or centre lock, the panel overlap changes — 85mm comes off the measured width in the calculation — so the lock is not free in terms of the opening it leaves you.

The Centre Lock

Mechanically the centre lock is the same handle and espagnolette. What changes is that it sits between two panels on the same rail, meeting near the middle of the opening, rather than closing against something fixed.

That suits a wide run where you want to open from the middle outwards — panels stacking at both ends rather than all at one — and it puts the handle where you naturally walk through, which on a five or six metre opening is a genuine ergonomic gain. It also means neither end of the run is committed to a locking profile against a wall.

The trade is that it introduces the visible profile into the middle of your view rather than at the edge of it, which on a structure specified for an uninterrupted outlook is worth thinking about from a chair before you commit.

What These Locks Actually Prevent

Time for some honesty, because this is where the trade tends to go quiet.

A lock on a glass sliding door is doing roughly the job of the little latch on a public toilet cubicle. It would not survive a determined shoulder, and it has never needed to. What it prevents is the far more common and considerably more irritating event: the door opening when nobody meant it to.

In practice that means the wind, which is the thing most likely to try your handle. An unlocked panel on a breezy night will run itself open and then closed again with a sound like somebody dropping a wardrobe. It means the dog, who has worked out that leaning on glass produces results. It means small children, who will find a moving panel more interesting than anything you bought for them. It means the neighbour's cat treating your veranda as an annexe. And it means the casual opportunist who tries a handle, finds it locked and moves on to somewhere easier, which is a genuine and underrated category.

What it does not do is turn a wall of glass into a strongroom. The panel beside the lock is 10mm toughened glass, and no closure device changes that. If you are storing something genuinely valuable out there, the honest answer is that the enclosure is the consideration rather than the ironmongery, and a well-lit space with nothing worth taking in it is doing more for you than a heavier lock ever would.

Which One for Which Garden

A few patterns hold up reliably.

If the doors get closed for the winter and opened again in April, and the requirement is mainly to stop the wind having them, a bolt lock is entirely adequate and the money is better spent elsewhere. This is the most common honest answer and the one least often given.

If the veranda is used daily, if children or older relatives will be operating it, or if it is the route between the kitchen and the garden, buy the side lock and enjoy having a handle.

If the run is wide, if you want to open from the middle, or if the natural walking line is the centre of the opening rather than one end, the centre lock is the one that suits the way you will actually move through the space.

And if the structure is genuinely open on other sides anyway, be honest that the lock is a convenience rather than a barrier, and choose it on that basis.

Three Things to Settle at Order Stage

Height first: both handle-based locks are made for installation heights up to 2500mm, which covers the standard range of a Fiano run but is worth confirming against your own figure.

Which side the key goes on, second. The handle operates from both faces, but the cylinder sits on one — and whether you want to be able to lock it from outside, or deliberately not, is a decision rather than a default.

And the installation itself, third. The assembly manuals and fitting videos are unusually blunt about it: tempered glass cannot be drilled, ground or cut, the profiles are shortened from the top rather than the bottom, the trackers that make the lock operate smoothly are ordered separately, and incorrect installation results in a broken lock that has to be replaced rather than adjusted. It is a small component with a specific method, and it is the one part of a self-build worth reading twice before picking up a drill.