The main parts of a door are the frame (head jamb, side jambs and sill), the panel or slab (stiles, rails and panels), the hardware (hinges, lockset, latch, deadbolt and strike plate), the glass (glazing, sidelights and transom), and the seals (weatherstripping, door sweep and threshold). Exterior doors add trim, brickmould and hidden flashing.
Most people learn the parts of a door the hard way. Something starts sticking, a draft shows up at the bottom of the entry, or a contractor says “astragal” and you nod along. Then the quote arrives and half of it is unreadable.
This guide covers door anatomy from top to bottom: every door part name, a labeled door parts diagram, plain-English definitions and the problem each part tends to cause. Some people say door pieces or door components; it all means the same thing. It covers the frame, the panel, the hardware, the glass, the weatherproofing and the trim. It also covers the pieces other glossaries skip: sill pans, multipoint locks, backset, and the difference between a rough opening and a door size. At the end, a symptom chart works backward from what your door is doing to the part responsible.
Key takeaways
- The frame, not the panel, causes most door problems.
- A jamb is one piece. The frame is the whole assembly of jambs and, on exterior doors, the sill.
- Weatherstripping and door sweeps wear out first, usually within 5 to 10 years, and cost little to replace.
- The sill pan and flashing are hidden after installation, and they decide whether an exterior door leaks in year five or lasts thirty.
Door Parts Diagram and Quick Reference
Figure 1. Door parts diagram: the main parts of an exterior door with a sidelight and a transom.
The diagram above labels the parts of an exterior door. The table below lists all the parts of the door: where each one sits, what it does, and the other names you will hear for it.
| Part | Where it is | What it does | Also called |
|---|---|---|---|
| Head jamb | Top of the frame | Caps the frame and carries the load above | Head, door head |
| Side jambs | Both sides of the frame | Support the panel and hold the hinges and strike plate | Hinge jamb, strike jamb |
| Sill | Bottom of an exterior frame | Seals the frame to the floor and sheds water | Door sill |
| Threshold | Cap over the sill | Takes foot traffic and blocks wind and water | Saddle |
| Door stop | Strip on the jambs | The closed panel rests against it | Stop moulding |
| Panel | The part that swings | The door itself | Slab, leaf |
| Stile | Vertical edges of the panel | Carry the hinges on one side and the lock on the other | Hinge stile, lock stile |
| Rail | Horizontal sections of the panel | Tie the stiles together and frame the panels | Top rail, lock rail, bottom rail |
| Mullion | Inside the panel, or between door and sidelight | Divides panels, or joins two units | Mull |
| Hinge | Between hinge stile and jamb | Lets the panel swing | Butt hinge |
| Lockset | Lock stile, about 36 inches up | Latches and locks the door | Handleset, hardware |
| Latch | Edge of the lock stile | Spring bolt that holds the door shut | Latch bolt |
| Deadbolt | Above the lockset | Solid bolt that resists forced entry | Dead bolt |
| Strike plate | On the strike jamb | Receives the latch and deadbolt | Strike |
| Bore hole | Through the lock stile | Opening drilled for the lockset | Cross bore |
| Weatherstripping | Around the frame | Seals the gap when the door is closed | Weather seal |
| Door sweep | Bottom edge of the panel | Seals the gap above the threshold | Door bottom, door shoe |
| Casing | Interior wall, around the frame | Hides the gap between frame and drywall | Interior trim |
| Brickmould | Exterior wall, around the frame | Hides the outside gap and backs storm doors | Exterior casing |
| Glazing | Inside the panel or sidelight | The glass | Glass, lite |
| Sidelight | Beside the door | Fixed glass panel that adds light | Side window, sidelite |
| Transom | Above the door | Glass that adds light and height | Transom window |
| Astragal | Between two panels on a double door | Covers and seals the meeting seam | Meeting-stile seal |
| Rough opening | In the wall framing | The framed hole the door unit installs into | RO |
| Sill pan | Under the sill, hidden | Catches water and drains it outdoors | Pan flashing |
Parts of an Exterior Door
An exterior door, including a front door, uses every part in the table and adds the ones that keep weather out. These are the parts of a front door, also called front door components, that an interior door does not have:
- Sill and threshold. The sill is the fixed bottom of the frame; the threshold caps it and slopes outward to shed water.
- Weatherstripping and a door sweep. One seals the sides and top of the panel, the other seals the bottom.
- Brickmould and a drip cap. Trim on the outside wall, with flashing above it that pushes water away.
- A sill pan and flashing. Hidden waterproofing under and around the frame.
- A deadbolt, and on tall or wide doors, a multipoint lock.
- Sidelights and a transom, which turn a single door into an entry system.
An interior door is simpler. It has a three-sided jamb, a door stop, and casing on both sides. It has no sill, threshold, weatherstripping, brickmould or flashing, and it is often hollow core. The sections below explain each part in detail, starting with the frame.
The Door Frame
The frame is the fixed part. It sits in the doorway, gets shimmed and fastened into the wall framing, and the panel hangs from it. When a door has problems, the frame is the culprit more often than the panel.
Head Jamb
The head jamb is the horizontal piece at the top of the frame. It is also called the head or the door head. On an exterior door it is usually the piece that flashing tucks behind, so if water shows up at the top corners of your entry, the head jamb detail is where a good installer looks first.
Side Jambs
The two vertical members of the frame. One is the hinge jamb, which carries the full weight of the panel through the hinges. The other is the strike jamb, which takes the impact every time the door closes and the latch drops in.
They are not interchangeable in what they go through. A hinge jamb that was not shimmed properly behind the hinge locations will let the door sag within a couple of years. On a heavy solid wood or steel door, it can happen in months.
Door Stop (Stop Moulding)
The door stop is the thin strip on the jambs that the closed panel rests against. It keeps the panel from swinging through the opening and sets how far the panel sits in the frame. On interior doors the stop is usually a separate strip of moulding. On many exterior frames it is milled into the jamb as a step, called a rabbet, so there is nothing to pry off.
Door Jamb vs. Door Frame
People use these interchangeably, and they are not the same thing. A jamb is one piece. The frame is the assembly. Two side jambs plus a head jamb make the frame, and on an exterior door the sill makes it four.
The distinction matters when you buy parts. “Replacing a jamb” can mean swapping one damaged leg. “Replacing the frame” means pulling everything, which is a different job and a different price.
Sill
The sill is the bottom member of an exterior door frame. It fastens to the subfloor and keeps water out at the base of the opening. Interior doors do not have sills.
Sills are the most neglected part of a door. Nobody looks at them until the floor near the entry feels soft. In Los Angeles the failure usually is not constant rain. It is a handful of hard storms a year hitting a sill that was never flashed correctly, plus irrigation overspray that nobody thinks about.
Threshold
The threshold is the cap that covers the sill. It is usually aluminum, sometimes fiberglass or oak, and it slopes toward the exterior so water runs off instead of pooling. Many thresholds have an adjustable insert you can raise or lower with a screwdriver to tighten the seal against the door sweep as the sweep compresses over time.
If you have a small draft at the bottom of your front door, adjusting the threshold is a ten-minute fix that most homeowners never try.
Mullion (Mull)
A mull is the joint where two units meet. When a door frame is joined to a sidelight frame, the seam between them is the mull. It is typically covered on both sides with a mull casing.
Confusingly, “mullion” also names a vertical divider inside a door panel. Two different parts, same word. Context tells you which one someone means.
Doorway and Rough Opening
The doorway is the opening you walk through. The framed hole in the wall, before the door unit goes in, is the rough opening. It is typically about two inches wider and two and a half inches taller than the door unit, which leaves room for shimming and squaring the frame.
This is the number that trips people up when they order a door from a measurement they took themselves. Measuring the visible opening between the jambs gives you the daylight opening, which is not the door size and not the rough opening. Our breakdown of standard door sizes covers the actual dimensions and how they relate to rough openings.
Casing and Brickmould (Door Trim)
Casing is the trim on the interior wall that hides the gap between the frame and the drywall. Brickmould is its exterior counterpart. It is a thicker profile that hides the gap on the outside, buffers the door against brick, stucco or siding, and is the surface a storm door attaches to. Brickmould is made of wood, aluminum, PVC, fiberglass or composite.
The Door Panel
Figure 2. Anatomy of a door panel: stiles, rails, mullion, hinges and bore holes.
The panel is the part that swings. It is also called the slab or leaf, especially when you buy it by itself without a frame.
Stiles
Stiles are the vertical members running the full height of both edges of the panel. The hinge stile is on the hinge side and the lock stile is on the handle side.
Lock stile width matters more than people realize. A narrow lock stile limits your hardware choices, because a multipoint lock or a mortise lockset needs enough material to accept the hardware without weakening the panel. If you are specifying a modern door with a slim profile, ask about lock stile width before you fall for a particular handle.
Rails
Rails are the horizontal members. A typical panel door has a top rail, a bottom rail, and often a lock rail (also called a mid rail) at roughly handle height.
Bottom rails are usually the widest, partly for proportion and partly because that is where the door takes the most abuse. On a Craftsman entry the bottom rail is often ten or twelve inches tall, which is part of what gives the style its grounded look.
Mullion (Panel)
Inside the panel, a mullion is a vertical divider between two smaller panels, running between rails. It looks like a stile but sits in the field of the door rather than at the edge.
Panel Core
What is inside the slab determines weight, sound blocking and security. There are three basic constructions:
- Hollow core: A honeycomb cardboard interior between two skins. Light, cheap, fine for closets and bedrooms. Blocks almost no sound.
- Solid core: An engineered wood or composite core between two skins. Heavier, much better acoustically, and the right choice for bathrooms, offices and any door where you want privacy.
- Solid wood: Stile and rail construction in real lumber. Heaviest, most expensive, and the only option with authentic grain on the edges.
The upgrade from hollow core to solid core on interior doors is one of the cheaper improvements to how a house feels. Manufacturers like TruStile build interior doors in both MDF and solid wood in the same profiles, so you can match the look across a house and spend more only on the doors where sound matters.
Bore Hole and Backset
The bore hole is the large hole drilled through the panel for the lockset, usually 2 1/8 inches. The backset is the distance from the edge of the door to the center of that hole, standard at either 2 3/8 or 2 3/4 inches.
If you buy a handle that does not fit, backset is almost always why.
Door Hardware: Hinges, Locks and Knobs
Hardware is where most of the wear happens. It is also the part you can see, touch and replace without removing the door.
Hinges
A hinge has three parts: two leaves, one screwed to the door edge and one to the jamb, and the knuckles that interlock between them, held together by a pin. The pin is why you can lift a door off its hinges with a hammer and a nail: tap it out from below and the leaves separate.
Three hinges is standard on an 80-inch door. Add a fourth on doors taller than about 7 feet or on heavy solid wood, steel or glass-filled doors, where the extra hinge shares the load and slows sagging.
The common types:
- Butt hinges: The standard flat-leaf hinge, mortised into the door edge and the jamb.
- Ball bearing hinges: Butt hinges with bearings between the knuckles. Smoother and longer lasting, and the right choice for heavy exterior doors.
- Concealed hinges: Hidden when the door is closed. Common on modern flush doors.
- Pivot hinges: Carry the door on a pin at the top and bottom instead of on the side. Used for oversized and statement doors.
- Spring hinges: Close the door automatically. Some building codes require self-closing doors between a house and an attached garage, so check what your jurisdiction requires before you choose.
The finish should match your lockset. A brushed nickel handle with oil-rubbed bronze hinges is one of the most common mismatches we see.
Lockset
Figure 3. Parts of a doorknob and lockset in cross-section, with backset marked.
The lockset is the complete assembly of handle, latch and lock. People call it a doorknob, but a lockset is the whole set of components that fit through the bore hole. The four basic functions:
- Entry: Locks with a key from outside and a button or thumb turn inside. This is what most front doors use, usually paired with a separate deadbolt.
- Privacy: Locks from the inside with no key. Bathrooms and bedrooms.
- Passage: Latches but never locks. Hallways and closets.
- Dummy: A handle that is fixed in place and does nothing. Used on the inactive side of a French door or as a pull.
Parts of a Doorknob or Door Handle
Whether it is a knob or a lever, the same components sit inside:
- Knob or lever: The part you grip and turn. Levers are easier on hands and are the standard for accessibility.
- Rose: The round or square plate that sits flush against the door face and hides the bore hole. Also called a back plate or escutcheon on some designs.
- Spindle: The square metal rod that runs through the door and connects the knob or lever on each side so both turn the latch.
- Latch assembly: The mechanism in the door edge that retracts when the handle turns.
- Cylinder: The keyed part of the lock, where the key goes in.
- Thumb turn or button: The inside control that locks and unlocks without a key.
- Strike plate: The metal plate on the jamb that the latch bolt enters.
Latch
The latch is the spring-loaded bolt on the edge of the door that holds it closed. A beveled face lets it slide over the strike plate and snap into the hole. It keeps the door shut but is not a security device. A credit card can often push a latch back, which is why entry doors also get a deadbolt.
Deadbolt
A deadbolt is a separate lock with a solid bolt that extends into the jamb and does not retract unless the key or thumb turn moves it. It sits about 5 1/2 inches above the lockset on most doors. A good deadbolt has a throw of at least 1 inch, meaning the bolt extends that far into the frame.
For security, the deadbolt matters less than what it goes into. A one-inch bolt held by a short screw in thin jamb wood is easy to kick through. See the strike plate section below.
Multipoint Lock
A multipoint lock engages the frame at several points, typically three: top, middle and bottom. One lever or handle throws all the bolts at once. These are standard on European-style and many modern doors, and common on French and tall entry doors. They pull the slab tight against the weatherstripping along its full height, which improves both security and air sealing on doors that tend to bow.
They need a wide enough lock stile and a frame prepared for them, so they are not a simple retrofit.
Strike Plate and Mortise Plate
The strike plate is the metal plate on the jamb with the opening the latch or bolt enters. It protects the wood and sets the position where the latch catches.
The term mortise plate gets used loosely. In most cases it refers to the faceplate on the door edge that covers the latch mechanism, not the plate on the jamb. If someone says mortise plate, ask which one they mean.
The cheap upgrade that matters: replace the short screws that come with strike plates with 3-inch screws that reach the wall stud behind the jamb. The standard 3/4-inch screws only bite into the jamb itself.
Escutcheon
An escutcheon is a decorative plate around a keyhole or handle. It also protects the surface from scratches and wear. On modern locksets the rose often does this job.
Thumb Turn
The thumb turn is the small lever or knob on the inside that locks and unlocks a deadbolt without a key.
Kick Plate and Door Viewer
A kick plate is a metal or composite panel fixed to the lower part of the door to protect it from shoes, carts and pets. A door viewer, also called a peephole, is the small lens set in the door at eye level so you can see who is outside. Wide-angle viewers show a 180-degree field. Many people now pair one with a camera doorbell.
Glass and Light: Glazing, Sidelights and Transoms
Glass is what turns a plain entry into one that lets daylight into the hall. It is also where energy performance, privacy and break-in resistance are decided.
Glazing and Lites
Glazing is the glass in a door. A lite (sometimes spelled light) is a single pane or opening, so a “half-lite door” has glass in the upper half and a “full-lite door” has glass nearly edge to edge. Most exterior glazing is a sealed insulated glass unit: two or three panes with a spacer and a gas fill between them.
Two things to ask about on any glass door:
- Low-E coating: A microscopically thin metallic layer that reflects heat. In Southern California it matters mostly for blocking solar heat gain and fading of floors and furniture, and it is how a glazed door meets California’s Title 24 energy requirements.
- Glass type: Tempered glass is required in doors by code, and breaks into small pieces. Laminated glass has a plastic interlayer that holds the glass together when broken, which adds security and sound reduction.
Sidelights
Sidelights are the narrow fixed windows on one or both sides of an entry door. If you have ever wondered what the windows on the side of a door are called, that is the answer. They sit in their own frame and join the door frame at the mull.
Sidelights bring daylight into an entry without adding a second door to maintain. Because they are glass at ground level next to the handle, many homeowners choose laminated or obscure glass for them. Anyone reaching through a broken sidelight can unlock a deadbolt, which is why a keyed deadbolt on the inside is a real security option on doors with sidelights.
Transom
A transom is a window above the door, set in the frame over the head jamb. Some are fixed and some open for ventilation. Transoms are common over interior doors in older buildings, where they let light and air pass between rooms, and over entries, where they add daylight above the door without making the door taller.
A half-circle window above a door is usually called a fanlight.
Grilles, Simulated Divided Lites and Muntins
The bars that divide a glass area into smaller panes are called muntins (or grilles). They come in three forms:
- True divided lites: Separate panes of glass joined by real muntins. Authentic, expensive and less energy efficient.
- Simulated divided lites (SDL): Muntins fixed to the outside and inside of a single insulated glass unit, sometimes with a spacer between them. They look like true divided lites and perform like one big pane.
- Grilles between the glass: Thin bars inside the sealed unit. Easy to clean, and visibly less realistic.
Muntins should not be confused with mullions, which join two separate units or panels.
Dentil Shelf
A dentil shelf is a small decorative ledge below a window or glass panel in a door, usually with small block-shaped supports under it. It is typical of Craftsman and Tudor style entries. It has no structural job.
Weatherproofing and Sealing
Figure 4. Exterior door sill cross-section, showing where water is meant to go.
Most exterior door failures are water failures. A door can be flawless and still rot its frame in a few years if the parts that manage water are wrong or missing.
Weatherstripping
Weatherstripping is the compressible seal around the door that closes the gap between the panel and the frame. It is usually foam, vinyl or rubber, installed on the jambs and head. Expect to replace it every 5 to 10 years. If you can see daylight around a closed door, or if the strip is flat and does not spring back when you press it, it is done.
Door Sweep
The door sweep is the seal fastened to the bottom of the panel that closes the gap between the slab and the threshold. A good sweep is the cheapest improvement for a drafty door. If the sweep is worn, the fix takes minutes and needs only a screwdriver.
Astragal
An astragal is a vertical strip of trim or weatherstripping where two doors meet in the center, on a double door or a French door. The inactive leaf usually carries it. It closes the gap between the leaves and gives the active leaf something to close against.
Sill Pan and Flashing
A sill pan is a waterproof tray installed under the door sill before the door goes in. It catches any water that gets past the threshold and directs it back outside. Flashing is the waterproof membrane or metal that wraps the rough opening so water is led over the outer face of the wall, not behind it.
These are the parts you will never see in a finished house and the ones that decide whether the subfloor under your entry lasts 30 years or 5. They are also the most common thing skipped on a quick replacement. If you are comparing bids, ask whether a sill pan and flashing are included.
Drip Cap
A drip cap is a small sloped piece of metal or moulding above the door, fixed to the outside of the head jamb. It sends water running down the wall away from the top of the door instead of letting it drip into the frame.
Parts of Sliding, Patio, French and Double Doors
These doors share most of the parts above, with a few of their own.
Sliding and Patio Door Parts
| Part | What it does |
|---|---|
| Active panel | The sliding panel you open and close. |
| Fixed panel | The panel that stays in place. |
| Track | The channel the active panel rolls along, set into the sill. |
| Rollers | The wheels at the bottom of the panel that carry its weight along the track. |
| Head track | The upper channel that keeps the panel upright and in line. |
| Interlock | The vertical strips where the sliding and fixed panels meet and seal against each other. |
| Handle and latch | Pulls the panel and locks it to the frame. |
| Weatherstripping | Pile or foam seals along the panel edges and track. |
| Weep holes | Small drain slots in the track that let water escape. |
| Screen door | A removable screen panel that runs on its own track. |
When a sliding door starts to stick, the problem is almost always the track or the rollers. Dirt and debris in the track make the panel drag, and worn rollers make it wobble and scrape. Both are cheap to fix compared with replacing the door. Keep the weep holes clear: if they clog, water backs up in the track instead of draining.
Multi-slide and folding patio doors add more panels that stack or fold to open a wide wall of glass. They use the same parts, with more tracks and more hardware to maintain.
French and Double Door Parts
A French door has two panels hinged on opposite sides of one opening, usually with glass lites running most of their height. A double door is the same arrangement with any panel style, glass or solid.
Three terms matter here:
- Active leaf: The panel you open day to day. It carries the handle and the lock.
- Inactive leaf: The panel that stays closed until you need the full opening. It is held shut with flush bolts, small bolts set into the top and bottom edges that drop into the head jamb and the floor or threshold.
- Meeting stiles: The two stiles where the leaves meet in the center, usually sealed with an astragal.
If the inactive leaf is not bolted securely at the top and bottom, the whole door can feel loose, and the active leaf will not seal properly against it.
Prehung vs. Slab: What You’re Actually Buying
A slab is just the door panel: no frame, no hinges installed, and often no bore hole for the lockset. A prehung door is the complete unit: a panel already hung in its frame on hinges, with the bore hole drilled and the weatherstripping in place.
The choice depends on what is wrong with your door:
- Slab only: Works when the existing frame is square, solid and dry, and you only want a new look or a new panel. It is cheaper and quicker, but it assumes the frame is in good shape and that the new slab matches the old hinge locations and bore hole.
- Prehung: The right choice for most exterior replacements, because it gives you a new frame, a new seal and a door that is already fitted to it. It costs more and takes more work to install, since the old frame comes out.
If the frame is rotten, sagging or out of square, a new slab in an old frame will have the same problems the old one did.
Door Handing and Swing
Figure 5. Door handing: left hand, right hand, and their reverse versions, viewed from outside.
Handing tells you which way a door is hinged and which way it swings. You need it for any replacement order, and getting it wrong is the most common reason a new door arrives that cannot be installed.
How to determine handing: Stand outside the door, facing it from the side people approach it from. If the hinges are on your left, it is a left hand door. If the hinges are on your right, it is a right hand door.
In-swing and out-swing: Standard left hand and right hand doors swing in, opening into the house. Most front doors are in-swing, which keeps the hinges and hardware protected from weather and tampering. A door that swings out, toward you as you stand outside, is called reverse: left hand reverse has hinges on the left and opens outward, and right hand reverse has hinges on the right and opens outward. Out-swing doors are common on patios and in places where interior space is tight.
Manufacturers use slightly different conventions, so if you are unsure, take a photo from outside and send it with your order.
Which Door Part Is Failing?
Use this chart to match what you see to the part most likely responsible.
| What you notice | Likely part | Usual fix |
|---|---|---|
| Draft or daylight at the bottom of the door | Door sweep or threshold | Replace the sweep or raise the threshold insert |
| Draft or daylight along the sides or top | Weatherstripping | Replace the weatherstripping |
| Door sticks, rubs at the top corner on the latch side | Hinges or hinge jamb (sagging) | Tighten or replace hinges, shim the jamb, or replace the frame if it has moved |
| Latch does not catch, or the door will not stay closed | Strike plate or latch | Realign or replace the strike plate; adjust the door |
| Key sticks or the lock is stiff | Lock cylinder | Lubricate, or replace the cylinder or lockset |
| Handle is loose or wobbles | Rose, spindle or mounting screws | Tighten the screws; replace the lockset if worn |
| Soft or spongy floor near the door | Sill, sill pan or flashing | Inspect for rot; usually needs a full frame replacement |
| Stained or rotting wood at the bottom of the frame or trim | Sill, threshold, brickmould or casing | Replace the affected parts and fix the water source |
| Panel is bowed or warped | Panel (often UV, heat or moisture) | Replace the panel; a better finish or a shaded entry slows it down |
| Fogging between the panes of glass | Insulated glass unit (failed seal) | Replace the glass unit |
| Sliding door drags or jumps | Track or rollers | Clean the track, replace rollers |
Two notes. Wood and dark-painted doors that face the afternoon sun in Southern California can warp from UV and heat alone, so a warped panel is not always an installation problem. And fog between the panes cannot be wiped off, because it is inside the sealed unit: it means the seal has failed and the glass unit needs replacing.