Sash Window Parts
A glossary of traditional sash window components to help identify parts for repair or sourcing replacements.
Last reviewed: 15 June 2026 | 3 min read
Main structural components
Sash: The movable frame that holds the glass panes. Traditional windows have two sashes (top and bottom).
Box frame: The outer frame built into the wall opening, containing concealed pockets for the counterweights.
Jamb: The vertical side pieces of the box frame.
Head: The horizontal top piece of the box frame.
Sill: The horizontal bottom piece, typically sloped outward for water runoff. Most vulnerable to rot.
Sash components
Top rail: The horizontal timber at the top of a sash.
Bottom rail: The horizontal timber at the bottom of a sash. Often thicker than the top rail (40-50mm vs 30-40mm).
Meeting rail: The central horizontal rail where top and bottom sashes overlap when closed. The meeting rails of both sashes are usually beveled to create a weatherproof seal.
Stile: The vertical side pieces of a sash. Connect the rails.
Glazing bars (muntins): The slender timber bars dividing the glass into multiple panes. Georgian bars are typically 12-18mm wide.
Sash horn: Projecting pieces at the top corners of Victorian and later sashes, providing additional support for mortise and tenon joints on larger, heavier sashes.
Beads and trim
Staff bead (inner bead): The removable trim piece on the interior face of the frame that holds the inner (bottom) sash in place. Typically 12-15mm square section. Removal allows the bottom sash to be lifted out.
Parting bead (parting slip): The central vertical strip separating the two sashes. Sits in a groove in the jamb. Removal allows the top sash to be removed. Typically 8-10mm wide.
Outside lining: The external trim covering the joint between frame and masonry.
Counterbalance mechanism
Sash weight: Cast iron cylindrical weights, usually 75-100mm diameter, 200-300mm long, weighing 2-4 kg each. Two weights per sash, totaling the sash weight.
Sash cord: Connects the sash to the weights. Traditionally waxed flax (12-15mm diameter), now often synthetic cord. Wears through at the pulley after 20-40 years.
Pulley: Small wheel (brass or nylon) mortised into the top of the jamb. The cord runs over the pulley, changing direction from the sash edge to the weight pocket. Georgian pulleys are often brass with ceramic or hardwood wheels. Modern replacements use nylon wheels.
Pulley stile: The vertical timber piece in the jamb that houses the pulley wheel.
Weight pocket: The concealed compartment within the box frame where the weights travel up and down. One pocket on each side of the window.
Pocket piece (pocket cover): A removable panel on the internal face of the jamb, providing access to the weight pocket for repairs. Usually held by two screws, often painted over.
Glazing components
Glass (glazing): Georgian windows used hand-blown cylinder glass. Victorian windows used larger sheets of blown or early float glass. Modern replacements use float glass, though reproduction cylinder glass is available for conservation work.
Putty (glazing compound): Linseed oil putty for traditional timber windows. Requires painting after 2-3 weeks to seal.
Sourcing replacement parts
Specialist suppliers (Mighton Products, Ventrolla, Sash Window Workshop) stock sash cords, pulleys, weights, beads, and glazing bars. For listed buildings, match original profiles and materials.
- SPAB, "The Repair of Wood Windows" technical note
- Historic England, "Traditional Windows" (2017)
- Building Conservation Directory component glossary