Door Preparation 2026: The 161 Bore, the 86 Mortise Pocket, and What "Prepped For" Actually Guarantees
A door arrives on site "prepped", and whether the lock fits is decided by holes cut weeks earlier in another factory. This page sets out the standard bored-lock and mortise-lock preparations with their dimensions, explains the ANSI/BHMA A115 series that governs them, and lists the five things a purchase order has to say before a door manufacturer can cut anything.
Johnson LiuDigital Communications, Canton HylandMA Digital Media, Johns Hopkins University
A door is cut before the hardware arrives. That single fact governs everything on this page, because it means the specification has to be complete at the moment the door is ordered — not at the moment the lock is.
A door cut wrong is not adjustable. A bore that is 6mm out of position cannot be moved; the door is scrap or it gets a cover plate, and a cover plate on a specified building is a conversation nobody wants to have.
WHAT THE PREP NAMES MEAN
The North American trade refers to door preparations by shorthand numbers, and two of them cover most architectural openings.
The 161 preparation is the standard bored or cylindrical lock prep. It is a cross bore through the face of the door, a smaller edge bore through the door's edge into it, and a latch face cut-out.
The 86 preparation is the standard mortise lock prep. It is a rectangular pocket cut into the door's edge to take the lock case, with holes through the face for the spindle and cylinder, and a cut-out for the forend.
These preparations, and the frame preparations that go with them, are governed by the ANSI/BHMA A115 series of door and frame preparation standards. The value of a standard here is not the number itself but the fact that a door manufacturer in one country and a lock manufacturer in another can both work to it without speaking.
THE 161 BORE, DIMENSION BY DIMENSION
The cross bore is 2-1/8" (54mm) in diameter, drilled through the face of the door. This is the hole the lock chassis passes through, and it is the dimension that has effectively become universal on bored locks worldwide.
The edge bore is 1" (25.4mm) in diameter, drilled into the edge of the door until it meets the cross bore. This takes the latch.
The backset positions the centre of the cross bore from the edge of the door. In North America it is 2-3/8" (60mm) or 2-3/4" (70mm); elsewhere 60mm and 70mm are the same two positions arrived at from the other direction.
The latch face cut-out is a shallow mortise on the door edge for the latch faceplate, and it comes in two shapes — square corners or radius corners — for the same reason strike plates do: a router cannot cut a sharp internal corner. Getting this one wrong does not stop the door working; it leaves a visible gap.
THE 86 MORTISE POCKET
The pocket is a rectangular cavity in the door edge, and the figure normally quoted is 1-1/8" (29mm) wide by 8" (203mm) high, with the depth set by the lock case.
The width is the number that matters most, because it has to match the lock case thickness with a working clearance and no more. A pocket cut too wide leaves a lock that can rock in the door; too narrow and the case will not enter.
Through the face of the door there are then holes for the spindle and, where the lock is keyed, for the cylinder. Their positions are set by the lock's own geometry — the backset and the centre distance between spindle and cylinder — which is why a mortise lock cannot be substituted for another brand's without checking both.
The centre distance is the specific dimension that catches people. Two mortise locks with the same backset can have different distances between the spindle and the cylinder, and a door prepped for one will have a cylinder hole in the wrong place for the other. This is covered in more depth on our backset and centre-distance page.
PREPARATION IS NOT ONLY THE LOCK
A complete door preparation covers more than the lock, and the items that get forgotten are the ones with no obvious owner.
Hinge preparation — the number of hinge mortises, their size, their positions from the top of the door, and their corner treatment. Get the count wrong and the door arrives with three mortises when the schedule called for four.
Closer preparation — reinforcement inside the door for the closer's fixings, and on a hollow metal door that reinforcement is welded in during manufacture and cannot be added afterwards.
Exit device preparation — through-bolt holes, and reinforcement, positioned to the specific device. Exit devices are among the least interchangeable products in the catalogue.
Flush bolt and coordinator preparation on pairs. Vision panel cut-outs. Undercut for floor finishes and air transfer.
WHAT "PREPPED FOR" GUARANTEES, AND WHAT IT DOES NOT
A door described as "prepped for 161" guarantees the bore dimensions and the backset stated. It does not guarantee that a specific lock will fit, because a lock can be within the 161 family and still differ in the things the preparation does not describe — the rose or escutcheon footprint, the through-bolt positions, the door thickness range the chassis covers.
A door described as "prepped for mortise" guarantees a pocket. It does not guarantee that a specific mortise lock will fit, because the face holes are lock-specific.
The safe procedure is the one that sounds excessive and is not: send the lock manufacturer's template, or the lock's dimensioned drawing, to the door manufacturer, and have the door manufacturer confirm against it in writing. A template is a one-page document. A container of doors cut to the wrong centre distance is not recoverable.
THE FIVE LINES A DOOR ORDER NEEDS
Door thickness, in millimetres or inches. It determines whether the lock chassis will reach and whether the spindle is long enough.
Backset. The position of the bore from the door edge.
Preparation type, named — bored to the 161 pattern, mortise to a stated pocket size, or a specific manufacturer's template.
Handing, stated in the convention you are using, and stated as a convention. Our handing page covers why EU and North American handing can describe the same door with different words.
Fire rating, if any. A fire-rated door's preparation is part of its tested configuration, and cutting a hole in it that the test did not include is a change to the assembly.
WHY WE PUBLISH DRAWINGS RATHER THAN DESCRIPTIONS
Everything above is a reason a product description is not enough. A description says "mortise lock, 60mm backset". A drawing says where every hole goes.
Our product pages carry the dimensions we measure and supply, and where a drawing exists it is the authority. Where we do not have a published dimension, the row is absent — a door is cut once, and a plausible number in a specification table is worse than a missing one, because a missing number gets queried and a plausible one gets drilled.
Questions this answers
What is a 161 door preparation?
The standard bored or cylindrical lock prep: a 2-1/8" (54mm) cross bore through the face of the door, a 1" (25.4mm) edge bore into it from the door edge, and a latch face cut-out. The backset positions the cross bore at 2-3/8" (60mm) or 2-3/4" (70mm) from the edge.
What are the dimensions of a mortise lock pocket?
The commonly quoted figure is 1-1/8" (29mm) wide by 8" (203mm) high, with the depth set by the lock case. The width matters most — it has to match the case thickness with a working clearance and no more, or the lock rocks in the door.
Does "prepped for mortise" mean any mortise lock will fit?
No. It guarantees a pocket, not the holes through the face. The spindle and cylinder holes are set by the lock's own backset and centre distance, and two mortise locks with the same backset can have different centre distances. Send the lock's template to the door manufacturer and get written confirmation.
What does the ANSI/BHMA A115 series cover?
Door and frame preparation standards. Their value is not the numbers themselves but that a door manufacturer in one country and a lock manufacturer in another can both work to the same preparation without needing to speak to each other.
What gets forgotten on a door preparation order?
The items with no obvious owner: hinge count and positions, closer reinforcement (welded in during manufacture on hollow metal doors and impossible to add later), exit device through-bolts and reinforcement, flush bolt and coordinator prep on pairs, vision panels and undercut.
Can a door that has been cut wrong be fixed?
Rarely well. A bore 6mm out of position cannot be moved — the door is scrap or it gets a cover plate. This is why the specification has to be complete when the door is ordered, not when the lock is, and why sending the lock template to the door manufacturer is cheap insurance.
About Canton Hyland — Canton Hyland manufactures panic exit devices, locks and architectural door hardware for commercial and institutional projects, supplying specifiers and distributors internationally.