Measure it closed.
That sounds almost too simple, but measuring a friction stay correctly means identifying several specifications that work together: the closed track length, folded stack height, sash opening direction, hinge function, handedness, fixing pattern and expected sash load.
Miss one, and the replacement may not close.
The hard truth is that a well-made hinge can still be completely wrong for the window. A 16-inch friction stay with the wrong stack height can hold the sash yet leave the weather seal compressed unevenly. An egress hinge may open widely but fail to produce the legally required clear opening. A restricted stay may look safe while its release mechanism or fixings are unsuitable for the application.
So why do buyers still send suppliers one blurry photograph and ask for “the same hinge”?
When I review a friction stay specification, I treat a photograph without dimensions as supporting evidence, not identification. The minimum useful record is:
That is the difference between measuring a component and specifying a working window system.
A friction stay is a multi-link window hinge that supports the sash while controlling its movement through friction in the slider mechanism. CHIER’s window hinges and four-bar friction stays include compact, extended-arm, long-track and multi-link designs, which shows why visual similarity alone is unreliable: linkage geometry and mounting dimensions can differ even when two products appear nearly identical.
Open the window far enough to see the complete metal base channel. Measure the channel from one physical end to the other, preferably with the friction stay fully closed or removed and placed on a flat surface.
Measure the track. Not the arms.
Do not follow the articulated linkage around its pivots, and do not measure only between the first and last screw holes. Suppliers normally identify friction stay length by the nominal length of the base track.
Record the result in both millimetres and inches:
| Nominal size | Metric equivalent | Typical use |
|---|---|---|
| 8 inches | 203.2mm | Small top-hung vents |
| 10 inches | 254mm | Compact top-hung or selected egress systems |
| 12 inches | 304.8mm | Top-hung and side-hung windows |
| 16 inches | 406.4mm | Larger side-hung and top-hung sashes |
| 20 inches | 508mm | Tall or heavier top-hung sashes |
| 24 inches | 609.6mm | Large top-hung applications |
These are common catalogue sizes, not a universal compatibility chart. One Mila range lists top-hung friction stays in 8, 10, 12, 16, 20 and 24 inches, while its side-hung models are concentrated around 12 and 16 inches. The same catalogue changes allowable sash weight and opening angle by model, proving that nominal length is only one selection factor. Review the manufacturer’s friction-hinge data here.
Some retail measuring guides advise recording the length to the nearest whole inch—for example, treating 11.9 inches as a nominal 12-inch stay. That is useful for initial identification, but I would never approve an order from the rounded number alone. Compare the actual millimetre length, fixing pattern and technical drawing before purchase.
Stack height is the total folded thickness of the friction stay when its arms are completely closed on top of the base track.
Close the stay fully. Place one calliper jaw against the lowest surface and the other against the highest folded arm. Keep the calliper square; measuring at an angle can turn a 13mm assembly into an apparent 14mm or 15mm reading.
Mila’s fitting instructions define stack height as the measurement from the bottom arm to the top arm with all hinge arms folded together. They identify 13mm and 17mm as standard friction stay stack heights. See the fitting instructions.
The difference is only 4mm.
It is not minor.
| Stack height | Common application | What happens when incorrectly specified |
|---|---|---|
| 13mm | Shallower hardware cavities and many standard PVC-U systems | A replacement may sit too low in a cavity designed for a taller stack |
| 17mm | Deeper cavities or systems requiring a higher sash position | A replacement may bind, prevent closure or over-compress the gasket in a 13mm system |
| 16–18mm variants | Selected aluminium, heavy-duty and highline systems | Assuming every window uses 13mm or 17mm can produce an expensive mismatch |
The industry often talks as though only 13mm and 17mm exist. That is convenient, not completely true. Securistyle lists systems for 16–18mm hardware cavities, while its Defender data includes nominal 13mm, 16mm and 17mm variants.
And here is another common trap: a plastic packer underneath the stay is not automatically part of the hinge’s manufactured stack height. Record the hinge stack and any separate frame packer as two measurements. Otherwise, the supplier cannot tell whether you need a taller hinge, a standard hinge with packers, or a different profile connection.
Stand inside the building and look at how the sash moves.
A top-hung window is hinged along its upper edge. Its lower edge moves outward, like an awning window. The pair of friction stays normally runs along the two vertical sides of the sash.
A side-hung window is hinged along one vertical edge and opens outward like a door. Its friction stays normally sit across the upper and lower edges of the sash.
Simple, right?
Yet “top-hung friction stay” is often misread as “a hinge fitted at the top.” That mistake reverses the classification. The term describes the sash’s hinged edge, not merely the physical position of one track.
The distinction affects linkage geometry, opening angle and load direction. CHIER’s compact four-bar window friction stay therefore asks buyers to confirm track length, folded stack height, opening direction, sash dimensions, sash weight and opening angle before selection.
Length and stack height tell you whether the stay may fit. Opening function tells you whether the completed window will behave as intended.
A standard friction stay supports normal top-hung or side-hung window operation without an integrated safety restriction or special escape geometry.
Do not read “standard” as “suitable for everything.” Manufacturers publish different sash-height, sash-width, weight and opening-angle limits for each stay. Even within one product family, an 8-inch top-hung stay may open to a different angle and carry a different load than a 20-inch version.
For narrow tracks or unusual profile clearances, compare the existing component with an adjustable-slider multi-link friction stay and request a dimensioned drawing rather than relying on the product photograph.
An egress friction stay changes the opening geometry so a side-hung sash moves farther away from the frame, producing a larger unobstructed escape opening. Many egress products approach an 80° to 90° opening, although the exact angle depends on stay length, sash dimensions and manufacturer design.
But an egress label is not a building-control certificate.
In England, government-backed local building-control guidance states that an escape window should provide at least 0.33m² of unobstructed openable area, with neither clear dimension below 450mm; a 450mm-wide opening would need to be approximately 750mm high to reach 0.33m². The bottom of the openable area should generally be no more than 1,100mm above floor level. Oldham Council’s fire-escape window guidance sets out these measurements clearly.
Measure the clear opening after installation. Not the sash size. Not the frame aperture. Not the angle printed in the hinge brochure.
That distinction matters because an egress stay can open to 90° while a thick frame profile, handle position or projecting sash edge still reduces the usable escape route.
A restricted friction stay limits the initial window opening, commonly to 100mm, before a release mechanism allows additional movement for cleaning, maintenance or another approved purpose.
The 100mm figure is not marketing decoration. UK government guidance says a fixed restrictor limiting an opening to 100mm may avoid additional guarding requirements in certain overheating assessments, while openings wider than 100mm must follow the relevant protection-from-falling standards. Read the Approved Document O guidance.
Some commercial restricted stays are also tested against a 350N safety-device requirement and use an automatic re-engagement mechanism. Product data must be checked model by model; a release button, cable or catch does not automatically provide the same performance.
And restricted does not mean indestructible.
A UK Department of Health and Social Care alert followed a fatal fall from a second-floor hospital window after a restrictor was forced beyond its 100mm restriction. The alert warned that some devices could be inadequate against determined force.
The Health and Safety Executive also documented a fatal incident involving window side-stays fitted with plastic spacers that failed. That case is a blunt reminder that mounting details, spacer material and fixing strength can be as important as the stainless-steel hinge itself. Read the HSE safety notice.
Some products combine an initial restricted opening with a releasable egress or easy-clean function. These designs are often handed, meaning a left-opening sash and right-opening sash require different stays.
Do not guess the hand from the room side alone. Record:
Take photographs from inside and outside. A single front-facing photograph can reverse the apparent handing.
Photograph the closed window from inside, then photograph it partly open. Include the handle side, hinged side and both stays.
Do this first.
Once the sash is supported or a hinge has been removed, you may no longer have a clean reference for its original orientation, spacers and fixing positions.
Identify the edge around which the sash pivots. Write “top-hung” or “side-hung” on the measurement sheet rather than relying on memory.
For side-hung windows, also record left or right handing whenever the stay has egress, restriction or easy-clean functions.
Measure end to end along the base channel. Record the exact millimetre dimension and the likely nominal inch size.
Example:
Actual track: 411mmLikely nominal size: 16 inchesDo not order until drawing is checked
Fold the arms completely. Measure the total hinge thickness without including separate frame packers.
Record both:
Hinge stack: 13mmSeparate packer: 4mm
This is much better than writing “about 17mm.”
Open the sash slowly and watch its motion.
Function beats appearance. Two stainless-steel stays can have the same length and stack height while performing completely different jobs.
Measure sash width and height, then establish the glazed sash weight from drawings, glass build-up or a reliable calculation.
Record the centre-to-centre positions of fixing holes, track width, screw type, reinforcement location and clearance around the profile. CHIER’s quality-control and hardware testing process reflects the kind of system-level review buyers should request when repeat orders depend on stable dimensions and performance.
Never select load capacity by track length alone. As one example, Securistyle publishes top-hung systems rated from 120kg to 180kg depending on the product family, while side-hung limits and permitted sash dimensions differ sharply. Material, slider design, linkage geometry and sash proportions all matter.
A serious supplier enquiry should contain:
For a non-standard profile or private-label programme, submit these details through CHIER’s OEM/ODM hardware development service rather than asking a factory to reverse-engineer the application from one loose sample.
Bad measurement creates rattling sashes, poor gasket compression, difficult closing and unnecessary callbacks. But the larger issue is predictable movement under real use.
The U.S. Consumer Product Safety Commission reported that an estimated 5,600 children aged 12 and under received emergency-department treatment after falling from windows in 2024. About one in three required hospitalization, and the agency knew of at least 25 deaths between 2021 and 2023 involving children in that age group. Read the CPSC’s 2026 Window Safety Week release.
Those figures do not prove that friction stays caused the incidents. They prove something more basic: window-opening hardware is part of a safety system, and casual substitution is irresponsible.
Here is my unpopular opinion: “It fits the screw holes” is one of the weakest acceptance standards in the hardware trade.
A replacement should also:
Anything less is a visual repair, not a verified hardware replacement.
Measuring a friction stay means recording three matched specifications—closed track length, folded stack height and sash opening type—then confirming handedness, sash weight, frame cavity, fixing-hole pattern and any egress or restriction function before ordering a replacement for that exact window system.
Measure the metal base track from end to end, close the stay fully and measure its total folded thickness with a calliper, then identify whether the sash is top-hung or side-hung. Compare every result with a supplier drawing rather than ordering by nominal length alone.
Friction stay stack height is the total thickness of the hinge arms and base track when the stay is fully folded closed, measured from the bottom surface of the lowest arm to the top surface of the highest arm, without including unrelated frame packers or profile accessories.
The most common replacement sizes are 13mm and 17mm, although selected highline and heavy-duty systems also use 16mm or other cavity-specific dimensions.
A 13mm friction stay and a 17mm friction stay perform the same basic job, but their folded thicknesses suit different frame cavities; fitting the wrong stack can prevent full closure, distort gasket compression, misalign locks or force installers to improvise with unsuitable packing.
The 4mm difference changes the sash’s installed position relative to the frame. Measure the existing hinge itself and list separate packers independently.
A top-hung window is hinged along its upper edge and opens outward at the bottom, while a side-hung window is hinged along one vertical edge and opens outward like a door; replacement friction stays must match that movement geometry and the resulting direction of load.
Do not classify the window by where one visible track happens to sit. Classify it by the sash edge around which the window pivots.
An egress friction stay is a side-hung hinge geometry designed to move the sash farther away from the frame and create a larger clear escape opening, but the word “egress” does not by itself prove that the completed window meets local fire-safety dimensions.
Measure the unobstructed opening after installation. In England, commonly cited guidance requires at least 0.33m² and no clear dimension below 450mm, subject to the building type and applicable regulations.
The correct friction stay length is normally the end-to-end length of the closed base track, rounded only according to the supplier’s sizing convention, then checked against sash size, weight, opening angle and manufacturer data rather than selected by nominal length alone.
Common nominal lengths include 8, 10, 12, 16, 20 and 24 inches, but not every length is available or approved for every top-hung, side-hung, egress or restricted application.
A restricted friction stay should not be replaced with a standard hinge unless the responsible designer, property manager or competent authority confirms that the safety restriction is no longer required, because removing the restriction may increase fall risk and change the window’s regulatory compliance.
Where occupant safety depends on a 100mm limit, the replacement must preserve the intended restriction, release behaviour, fixing strength and resistance to misuse.
Do not order from the photograph.
Close the friction stay, measure the full track, check the folded stack with a calliper, identify top-hung or side-hung operation, and document every egress, restriction and easy-clean feature. Then add the sash dimensions, weight, profile drawing and fixing pattern.
For replacement selection, project sourcing or a custom friction stay programme, send CHIER your measurements and window profile details for a compatibility and quotation review.
