How Can I Tell Whether My Sliding Patio Door Uses a Compatible Mortise Lock?

Open the door and look at its narrow edge: if you see a narrow faceplate with a hook that moves when you turn the inside thumb turn, the door uses a mortise hook lock. For the EASILOK A10 path, three checks decide compatibility: the faceplate, hub position and hook must suit a standard 45° keyway mortise lock; the handle holes must measure 3-15/16″ (100mm) center to center; and the door must be 38–70mm (1-1/2″–2-3/4″) thick.

Step 1: Confirm it is a sliding door with an edge mortise

Use this guide only when the active panel slides horizontally on a track, the handle sits on the face of the narrow stile, and the lock body is recessed into the stile’s edge. Do not apply it to hinged or French doors, storm doors, swinging entry doors with tubular latches, multipoint systems, or commercial storefront doors — those use different hardware even when the visible handle looks similar.

Step 2: The open-door observation

With the door open and only if you are authorized to inspect it, turn the inside thumb turn gently while watching the door edge. If a hook swings out of the faceplate, the door uses a hook-style mortise lock. If the thumb turn moves but the hook does not, the tailpiece is disengaged or the mechanism is damaged. If the hook moves fine while open but will not lock once the door is closed, suspect panel alignment, rollers, or keeper position before blaming the lock. Never force a binding mechanism. This is normal-operation observation, not a bypass procedure.

Step 3: Seven features to compare

1. Mortise faceplate. Photograph the plate on the door edge; record length, width, end shape, and screw positions. Similar faceplates can hide different lock bodies, so this is only the first reference.

2. Lock-body dimensions. If the lock can be removed through the normal service procedure, record height, width, and depth, plus any markings. Never enlarge the door cavity to force a different body in.

3. Operating-hub position. The inside thumb turn — and the outside key cylinder on a Keyed version — must meet the mortise lock at the correct hub. Measure the hub’s position relative to the handle holes and the door edge.

4. Tailpiece length. Measure the old tailpiece. Many legacy tailpieces are short and max out at 42mm doors — if your door is thicker than that, a short tailpiece is likely why the old handle never worked properly. That is exactly the case an extended-length tailpiece is made for: it drives the mortise latch on doors up to 70mm with no cutting.

5. Hook direction and travel. Record which way the hook faces, how far it projects, and where it enters the keeper. A matching hook outline does not prove the travel and engagement depth are right.

6. Frame keeper. The keeper must catch the hook at the correct height and depth. Loose screws, a sagging panel, worn rollers, or a shifted frame cause alignment failures no new mortise lock can fix.

7. Handle-side dimensions. For the A10 path: 3-15/16″ center-to-center handle holes and 38–70mm structural door thickness. Do not substitute handle length or hole-edge distance for the center-to-center measurement, and do not count weatherstripping as door thickness.

Step 4: The “key turns but won’t lock” check

This is the most misdiagnosed symptom on keyed patio handles, and the most common one-star complaint on legacy sets. Two tailpieces must meet perfectly inside a tight mortise: cut 1mm too long and it binds, cut 1mm too short and it slips — so the key spins without locking, and owners assume the lock is broken. The actual fix is not a new lock but a connection that tolerates error: a 12mm receiving sleeve on the thumb turn that absorbs the length difference, plus a detachable tailpiece that can be removed for standard doors so nothing collides inside the lock.

Keyed or Non-Keyed: which configuration fits your door?

Both versions drive the same 45° keyway mortise hook lock from the inside thumb turn; they differ only in outside access. Choose Keyed when someone must lock or unlock from outside with a physical key. Choose Non-Keyed when the outside needs only a pull. Either way, the three hard dimensions above still have to match.

Signs this path is not a match

Pause and use a different guide when: the panel swings instead of sliding; there is no recessed mortise lock in the door edge; the holes are not 3-15/16″ center to center (Andersen gliding doors, typically 5-1/2″, are a common example); the door is outside 38–70mm; the hub does not align with the handle connection; the mortise body cannot fit the cavity without modifying the door; or the hook/keeper geometry is fundamentally different.

Frequently Asked Questions

Does the same hook shape mean two mortise locks are compatible?
No. Faceplate, body dimensions, hub position, tailpiece, hook travel, keeper, and handle-side dimensions must all match. Similar hooks can belong to incompatible mechanisms.

Can a keyed patio handle work with any mortise lock?
No. The cylinder’s tailpiece must engage the correct hub at the right position and depth without binding — and the 3-15/16″ spacing plus 38–70mm thickness still apply.

My door is 60mm thick. Will a standard replacement set fit?
Most standard sets top out around 1-3/4″ (44mm) because their tailpieces are too short. Measure your old tailpiece: if the door is thicker than about 42mm and the tailpiece is short, you need an extended-length tailpiece rated to 70mm — with no cutting on a Non-Keyed set.

Bottom line

Bottom line: if your sliding patio door shows a mortise hook lock in the door edge, 3-15/16″ handle-hole spacing, and 38–70mm thickness, the EASILOK A10 replacement path fits — including doors up to 70mm thick that short-tailpiece handles can’t reach, with no precision cutting on the Keyed version.