Every Part of a Sash Window Named: A Working Glossary

"The thin bit of wood down the side has come away and now the top one rattles." That is a perfectly good description of a broken parting bead, and any joiner worth ringing will understand it. But you will get a straighter answer, and a more accurate quote, if you can name the piece of timber you mean.

This is a working glossary rather than an academic one. Every part below is named the way the trade names it, with what it does and what usually goes wrong with it. If you learn six terms, learn pulley stile, parting bead, staff bead, meeting rail, pocket and horn. Those six carry most conversations.

The box frame: a hollow case, not a solid one

The thing people call "the frame" is not solid. On a proper box sash it is a hollow timber case built into the wall, and the hollow is where the counterweights live. It is made up of separate boards, and each has a name.

• Pulley stile. The vertical board on each side that the sashes actually slide against, so called because the pulleys are let into the top of it. It faces into the opening and takes all the wear. A groove is worked into its face to receive the parting bead.
• Outer lining. The board on the outside face of the box, usually the one you see from the street running up the reveal.
• Inner lining. The matching board on the room side. The staff bead is nailed to it, or to the pulley stile, depending on how the window was made.
• Back lining. A thin board, often only 6mm to 9mm, closing the back of the box against the brickwork. It is the reason weights do not grind against rough masonry. On many windows it is the first thing to rot, because it sits nearest the damp wall and nobody ever paints it.
• Head, or soffit lining. The horizontal board across the top of the box.
• Cill. The sloping bottom member that throws water off. Underneath it there is usually a throat or drip groove, a small square channel routed across the underside about 12mm in from the outer edge, which stops rain running back along the timber and into the wall. Some windows also have a sub-cill, a separate weathering piece bedded below. If yours is soft, our article on why the cill rots before anything else explains what to look at first.
• Pocket, and pocket piece. A rectangle cut out of the lower part of each pulley stile, closed by a removable panel: the pocket piece. Take it out and you can reach in and lift the weights out. On original windows it is held by a single screw and a bevelled edge that traps it. On later ones it is often just wedged. It is invisible until you know to look, so run a fingernail down the pulley stile about 300mm above the cill and feel for the join.
• Parting slip, or wagtail. A loose strip of timber, roughly 6mm thick, hanging on a nail inside the box between the two weights. It keeps the front weight and the back weight from colliding and clattering as they pass. It is the single most commonly missing part in a London sash, and its absence is why a lot of windows sound like somebody dropping cutlery inside the wall.

The sashes: the two moving frames

Each sash is a frame in its own right, jointed at the corners with mortice and tenon and holding the glass in a rebate.

• Stiles. The two vertical members. On a Victorian sash they are typically around 45mm thick.
• Top rail and bottom rail. The horizontals. The bottom rail of the lower sash is usually deeper than the others because it sits on the cill and takes the water, and it is bevelled on its underside to match the cill slope.
• Meeting rails. The two rails that come together in the middle when the window is shut. They are cut with matching bevels, usually about 6mm of overlap, so that as the sashes close the bevels wedge against one another and pull the window tight. If your window rattles at the middle, those bevels have worn or the sashes have shrunk apart.
• Horns. The short projections at the ends of the meeting rails, running down past the rail on the upper sash and up past it on the lower. They are structural. They leave extra timber beyond the mortice so the joint does not shear as the sash gets heavier, which is why they arrive in the middle of the nineteenth century: once the duty on glass came off in 1845, panes got larger and considerably heavier, and the old joint needed help. They also date a window fairly reliably, as our piece on reading sash horns sets out.
• Glazing bars, also called sash bars, and astragals if you are north of the border. The slender moulded members dividing the glass. On a Georgian sash they can be as fine as 15mm to 20mm, moulded on the inside face and rebated on both sides for glass.
• Rebate. The step cut into the sash to receive the glass, typically 10mm to 12mm deep on an original window.
• Putty. The linseed oil and whiting compound that beds and weathers the glass. Back putty is the thin bed behind the glass; face putty is the visible triangular fillet.
• Cord groove and knot hole. A vertical channel routed into the outer edge of each sash stile, with a recess at the top where the sash cord is nailed or knotted in. If you can see a groove with three rusty nail heads and a frayed stub of rope, that is a cord that has parted at the pulley. The full cord replacement sequence runs through what has to come off, in order, to put a new one in.

Three strips of timber that decide how it runs

People underestimate the beads. They are the cheapest components in the window and they control almost everything about how it slides.

• Staff bead. The moulded strip on the room side that holds the inner sash in. It is nailed, usually mitred at the corners, and it is meant to come off. Prise it away and the bottom sash comes out. If your staff bead has been overpainted twenty times and someone has screwed it on, that is why the window has not been serviced in fifty years.
• Parting bead. The strip that sits in the groove in the pulley stile and separates the two sashes so they can pass each other. Sections vary by house and by period, but most sit around 8mm to 10mm thick by 20mm to 25mm deep, so measure the groove rather than assuming. It is a friction fit. It is not nailed and it is not glued.
• Slip bead, or glazing bead. A small moulded strip pinned in to hold the glass instead of face putty, used occasionally on later or previously repaired windows.

There is more on how the two beads control clearance, rattle and draught in our article on staff beads and parting beads.

The balance gear, hidden inside the box

None of this is visible with the window shut, which is why it is the part homeowners have no vocabulary for. It is also the part that fails.

• Axle pulley. A wheel on a spindle housed in a faceplate, let flush into the top of each pulley stile. Wheels are commonly 44mm to 57mm (1¾in to 2¼in) across, in brass, iron or nylon, with the better ones running on a proper bearing. The wheel is the thing that squeals, and it explains why a cord always frays at the pulley end first: that is the one point where the rope bends and unbends every single time the sash moves. Our piece on how pulleys wear covers what to do about a seized one.
• Sash cord. Braided waxed cotton, sold in the UK in 6mm, 7mm and 8mm; most modern cord has a synthetic core inside the cotton for strength. Makers rate them differently, so treat the published figures as a guide rather than a standard. Roughly, 6mm is rated for about 30kg a side, while 8mm is rated anywhere from 50kg to 75kg depending on whose data sheet you read. On a heavy ground-floor sash, go up a size rather than down. We use 8mm as standard on sash cord replacement work in London because the glass in a Victorian ground-floor window is rarely light.
• Sash weights. Long cylindrical weights in cast iron or lead, hung on the ends of the cords, two per sash. Cast iron is about 7.2 g/cm³ and lead about 11.3 g/cm³, which matters because a narrow box will sometimes only take enough mass if the weights are lead. The pair on the upper sash should come to fractionally more than that sash weighs, so it holds itself up instead of creeping down. The pair on the lower sash should come to fractionally less than that sash weighs, so it stays put instead of drifting closed. Half a kilo either way is the sort of margin joiners work to, not five.
• Sash fastener. The catch on the meeting rails. The common pattern is the Fitch fastener, a cam that rotates and draws the two meeting rails together as it closes, which is what tightens the window against rattle. A worn Fitch that no longer pulls the rails up is a frequent cause of a draughty middle joint.
• Sash lift, finger pull or sash eye. The handles on the bottom rail, or the ring pulls used to reach a top sash.
• Brighton bolt. A screw-down bolt through the meeting rails, common on older London windows, which locks the sashes together and can be set to hold the window ajar.

If you want the mechanism rather than the vocabulary, how a sash window actually works explains why the balance has to be so exact.

The quick reference

Using the right word when you ring a joiner

The point of all this is a better first conversation. A few examples of what to say instead of what people usually say:

1. Instead of "the window won't stay up", say "the bottom sash drops when I let go, and there is a broken cord in the left-hand groove". That is a cord job, and it tells us whether it is one cord or all four.
2. Instead of "it rattles", say "the parting bead is missing on one side" or "the Fitch fastener no longer pulls the meeting rails together". Those are two different repairs at two different prices.
3. Instead of "the bottom is soft", say "the bottom rail of the lower sash gives under a bradawl about 40mm in from the corner, and the cill under it is sound". That is the difference between a splice and a new sash.
4. Instead of "it's painted shut", say "the staff beads have been painted over and the sash has not moved since we bought the house". That sets expectations about how long the first hour takes.

If a quote arrives with items you cannot place, ask which of the parts above they refer to. A line reading "renew parting beads and overhaul balance to both sashes" is a specific, checkable piece of work. A line reading "service windows" is not.

And if the parts are past naming and into rebuilding, that is sash window restoration rather than a repair, and worth pricing as such. Our sash window repair service covers every London borough, but you will get a better quote from anybody, us included, if you can point at the timber and call it by its name.