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Brown wooden door frames and jamb detail

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Door Anatomy and Terms

Knowing the correct name for each door part prevents quoting errors, reduces back-and-forth with the factory, and builds instant credibility with contractors and installers.
A rep who does not know the difference between a jamb and a casing, or between a slab and a unit, will produce incomplete quotes and lose credibility on technical calls. This page defines every part you will reference in sales conversations, product configurations, and order entries.

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The Complete Glossary

The door slab is the moving panel itself — the part that opens and closes. It is measured separately from the frame or rough opening and is sized by width x height x thickness. Standard residential thickness is 1-3/4 inch for exterior doors and 1-3/8 inch for interior doors.
Solid wood door slab
The jamb is the vertical and horizontal frame members that surround the door slab. The side jambs run vertically; the head jamb runs across the top. Jamb depth (also called jamb width) must match the wall thickness so the finished unit sits flush with the drywall on both sides.Common jamb depths:
  • 4-9/16” for 2x4 framing with drywall
  • 5-1/4” for 2x6 framing with drywall
  • Custom depths for thick walls, stucco, or masonry
The threshold is the bottom transition piece at the base of an exterior door. It seals the gap between the door slab bottom and the floor. Thresholds come in different heights and styles depending on flooring transition and ADA requirements. Always confirm threshold type for exterior prehung orders.
The hinge side is where the door pivots. The strike side (also called the lock side) is the opposite side where the latch bolt seats into the frame. These two terms are referenced constantly in handing discussions and hardware placement.
Bore prep refers to the machined holes in the door slab for the handle and deadbolt. A standard single bore is 2-1/8” in diameter. Backset is the distance from the edge of the door to the center of the bore hole — typically 2-3/8” or 2-3/4”. This must match the hardware set being ordered.
A lite is a glazed opening in the door. Lite descriptions tell you how much glass is in the slab. Always confirm privacy level and whether the application requires insulated glass (exterior) or decorative glass (interior).
A sidelite is a fixed, glazed panel installed beside the main door slab. Sidelites are part of the full unit width calculation. Always include sidelite widths when determining the total configuration size.
The astragal is the vertical strip between two door slabs in a double door system. It provides a weather seal and meeting edge for the inactive panel. Some systems use a flush bolt astragal on the inactive leaf.
Casing is the interior trim that covers the gap between the jamb and the drywall. Brickmould is the exterior trim that covers the gap between the frame and the siding or masonry. On replacement jobs, always confirm whether existing casing is being reused or if new trim is needed.
The rough opening is the framed structural opening in the wall where the door unit is installed. It is always larger than the unit to allow for shimming and leveling. Measure width stud-to-stud and height from subfloor to header underside.
Weatherstripping is the compressible sealing material around the door perimeter that prevents air, water, and dust infiltration. On prehung exterior units it is typically factory-applied to the doorstop. Check condition on replacements — damaged weatherstripping is a common customer complaint.
The doorstop is the small strip on the inside face of the jamb that the door slab contacts when closed. It prevents the slab from swinging through and creates a surface for weatherstripping to compress against.

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Lite Descriptions Explained

Lite terminology tells a rep and a customer how much of the door panel is glass.
For exterior applications, all glass in a door slab must be insulated glass units (IGU) to meet energy code and prevent condensation. For interior applications, decorative, clear, or privacy glass are all acceptable.

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The Anatomy of a Full Door System

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Slab Components

  • Panel body (wood, fiberglass, or steel)
  • Stiles (vertical edges)
  • Rails (horizontal edges)
  • Core (solid, hollow, or foam-filled)
  • Glass lite (if applicable)
  • Lock bore (single or double)
  • Hinge prep

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Frame Components

  • Head jamb (top horizontal)
  • Side jambs (vertical, hinge and strike side)
  • Doorstop
  • Weatherstripping
  • Threshold (exterior only)
  • Casing or brickmould

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Quick-Reference: Parts to Measure

The fastest way to learn these terms is to use them on every call, even early in training. Ask the customer: “What condition is the jamb in?” or “Is there a threshold issue at the base?” — even if you know the answer. Practice the vocabulary daily.