Door Viewers: Door Thickness Range, Barrel Diameter and Viewing Angle

A door viewer only fits a door inside its published thickness range, so check that range before you look at the viewing angle. Our records give 30–50 mm for the 160° version of DV06, 35–55 mm for DV05, DV09, DV11 and DV12-S, and 60–100 mm for the long versions of DV05 and DV06. DV04 is telescopic and adjusts from 34 to 62 mm. If the door is thicker than the range, the two halves of the viewer cannot reach each other. If it is thinner, they bottom out before they clamp the two faces of the door.

The barrel diameter comes second, because it decides the drill bit. The brass viewers DV05, DV06, DV09 and DV11 are listed in 12, 14 and 16 mm. DV04 has a 14 mm barrel. DV08 SN and DV12-S are listed at 28 mm. The viewing angle comes third: 160°, 180° or 200°. A wider angle shows more of the landing, but the image gets smaller and more curved towards the edge.

How a door viewer is built

A door viewer is two threaded parts that close on the door from opposite sides. The outer part carries the wide-angle lens and the outer ring and goes in from the corridor side. The inner part is the eyepiece barrel. It screws into the outer part from the room side and is tightened with a screwdriver in its slot while the outer ring is held still. On most models the inner part also carries a cover. The two parts can only engage over a limited depth, and that depth is what the thickness range describes.

The optics work in one direction only. From inside, the occupant sees a reduced, wide image of whoever is outside. From outside, a person looking into the lens sees almost nothing of the room. A viewer is a way of seeing out without opening the door, and nothing in its function depends on its finish or its outline. The figures below are what decide whether it works on a given door.

Measure the door where the hole will be

Measure the thickness at the point where the viewer will go, not at the edge of the leaf. On a panelled door the center of the leaf can be a panel thinner than the stiles around it. On a door with a metal skin, a cladding sheet or an applied moulding, the thickness at the hole includes all of it. The figure that matters is the depth the drill will pass through.

Then compare that figure with the ranges, and watch the gaps between them. A 55 mm door sits at the very top of the 35–55 mm range. A door between 56 and 59 mm falls between 35–55 and 60–100, so neither the short nor the long version of DV05 or DV06 covers it. Of the models here, only DV04 covers that band in its published data, with its 34–62 mm adjustment and 14 mm barrel. A door at the end of a range is worth a second measurement before the line is ordered. Thin doors have fewer options. The lowest published figure in this group is 30 mm, on the 160° version of DV06, followed by DV04 from 34 mm. Our data for these models does not cover a leaf thinner than 30 mm.

The barrel diameter decides the drill bit

The hole has to match the barrel. If it is too large, the viewer can turn or sit off center once tightened. If it is too small, the barrel will not go through. For DV05, DV06, DV09 and DV11 the diameter is chosen at order: each record lists 12, 14 and 16 mm, but none says which diameter is paired with which thickness range or angle. Put all three figures on the same order line.

If you are replacing an existing viewer, measure the hole that is already in the door. A viewer of the same bore goes into it without new drilling. A smaller bore leaves a gap round the barrel, and a larger one means re-drilling a finished door. Either way, the existing hole should decide the diameter.

DV08 SN and DV12-S are listed at 28 mm, which is a much larger hole than the 12 to 16 mm brass models need. Our records do not publish a separate drilling size for these two. Confirm the bore with us before a door is drilled, especially a door delivered finished or veneered. A 28 mm viewer cannot directly replace a 14 mm one.

General drilling practice is the same at any size. Drill square to the face. On timber, drill from one side until the point just breaks through, then finish from the other side so that neither face splinters. A hole that runs at an angle stops the two halves of the viewer from lining up, and no amount of tightening fixes that.

Viewing angle: 160°, 180° or 200°

The angle sets how much of the space outside the door the occupant can see. A wider angle shows a caller standing to one side, not only someone standing square to the door. The cost is that the image shrinks and curves towards the edge. In our data, 160° appears only on DV06, in its 30–50 mm version. DV05, DV09 and DV11 offer 180° or 200°. DV08 SN and DV12-S are listed at 200° only.

Where the viewer looks onto a corridor, as on an apartment or hotel room door, a caller can stand beside the door rather than in front of it, and 200° shows that position. On a door that opens onto a shallow porch, where a visitor naturally faces the door, 180° is enough. Whichever angle you choose, check that the angle and the thickness range you want appear together in the same record. A 160° DV06 is the 30–50 mm version, not the 60–100 mm one.

Lens, cover, material and finish

Most of these records list a synthetic resin lens or lens cover. DV08 SN lists a glass lens. The cover sits on the room side and closes the eyepiece, so a lit room behind the door does not show at the lens outside. DV08 SN is offered with or without a cover. On DV06 the cover is listed as optional. DV09, DV11 and DV12-S list it as part of the viewer, and DV04 is described with an inside cover.

DV05, DV06, DV09 and DV11 are brass. DV04 and DV08 SN are zinc alloy, and DV12-S is ABS plastic in a BN finish. DV11 has a square outer face, as its photographs show. Its barrel is still listed in round diameters of 12, 14 and 16 mm, so the hole is drilled the same way as for a round viewer. Specify the finish to match the lever or knob on the same door. DV05 and DV06 list CP, PB, SC, SN, AB, AC and ORB among their finishes, and DV09 and DV11 list PB, AB, AC, CP and SN.

If you searched for DV08: the plain DV08 record lists its material as brass or zinc alloy, plus its finishes, but publishes no dimensions. DV08 SN is the record that carries the figures, 28 mm diameter, 60–95 mm length, 200° and a glass lens. The 60–95 mm figure is a length. Our record does not convert it into a door thickness range, so quote the measured door thickness when you ask about it.

Where it goes on the leaf

A viewer is fitted centered on the width of the leaf, at the occupant's eye height. Where children or seated users also need to see out, a second, lower viewer is a common answer. It does not go on the frame or close to the lock edge, and it should be the same finish as the rest of the hardware on that door.

What to put on the order

One line per door thickness, not one line per model. Each line should carry the measured thickness at the hole, the model, the barrel diameter, the length version or thickness range, the viewing angle, the lens and cover, and the finish. Entrance doors and internal doors on the same project often differ in thickness. If they share one order line, part of the delivery will not fit.

Our records do not publish the following: the viewing angle of DV04, a door thickness range for DV08 SN separate from its 60–95 mm length, a drilling size for the 28 mm models, and which diameter goes with which angle or range on DV05, DV06, DV09 and DV11. If any of these decide your order, ask for the figure in writing before the doors are drilled.