Door Preparation 2026: The 161 Bore, the 86 Mortise Pocket, and What "Prepped For" Actually Guarantees

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.

HYDE (Canton Hyland, Zhongshan, since 1998) is the door hardware factory that publishes this article.

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 center 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 161 template, in inches and millimeters

A 161 template is the one-page drawing that turns the dimensions above into drill positions: it is laid against the door face and edge, or built into a boring jig, so the cross bore, the edge bore and the latch face cut-out land in the right place relative to each other. The table collects the figures it carries. The fractions are the standard; the millimeters are conversions. The latch face and strike sizes are the ones commercial cylindrical locks in North America use; residential latches often have a smaller face, which is one reason the lock's own template outranks any table.

Where the centerline sits. Horizontally the template fixes one line, the cross bore center, at the backset from the door edge. Through the door it fixes another: the edge bore runs on the middle of the door thickness, so on a 1-3/4" door its center is 7/8" (22.2mm) in from each face. Vertically, the cross bore, the edge bore and the latch face share one centerline, and the strike on the frame has to sit on the same line or the latch rides on the strike lip. The height of that line above the floor is not part of the 161 bore pattern; it comes from the door and frame supplier's hardware locations, and in the United States the ADA places operable hardware between 34" and 48" (865 to 1220mm) above the finished floor.

Using it as a drilling jig. A boring jig is the 161 template in steel: it clamps over the door edge, is set to the backset, and guides a 2-1/8" hole saw through the face and a 1" bit into the edge. Drill the cross bore from one face until the pilot breaks through, then finish from the other face, so neither face splinters. Bore the edge into the cross bore, then rout the latch face cut-out to the faceplate's thickness so the faceplate sits flush.

Checking an existing door. Before ordering a lock for a door that is already bored, measure the cross bore diameter, the edge bore diameter, the door thickness and the backset. The center of a hole is hard to measure to, so measure from the door edge to the near side of the cross bore and add half the bore. Example: a reading of 33mm plus half of 54mm (27mm) is a 60mm backset; a reading of 43mm is 70mm. Then measure the latch face pocket against the faceplate of the lock you intend to fit; a pocket larger than the faceplate leaves the visible gap described above.

Which of our cylindrical locks publish matching figures. Our product data gives a backset for some heavy-duty cylindrical locks, and those backsets include the two 161 positions: the 5870 ACET and 5874 ACET list 60mm/70mm with a 35–50mm door thickness range, the 5831 SSET lists 60 / 70 / 80 / 90 mm adjustable and 35–50 mm, and the 5870 SSPS lists 70mm. A 35–50mm range includes a 1-3/4" (44.5mm) door. Our data does not publish a cross bore diameter, an edge bore diameter, a latch face size or a strike size for these models, so a matching backset is not a statement that they fit a 161 prep; ask for the lock's template and check the bores against it before a door is cut.

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 center distance between spindle and cylinder) which is why a mortise lock cannot be substituted for another brand's without checking both.

The center 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 catalog.

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 center distance is not recoverable.

The five lines a door order needs

Door thickness, in millimeters 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.