A 4-bar hinge supports and guides an operable window sash as it opens away from the frame. Because replacement hinges can differ in track length, bar width, stack height, mounting-hole pattern, handing, and opening geometry, several measurements should be compared before selecting a replacement.

Before You Start

Tools and information you may need:

• Tape measure or rigid ruler
• Digital caliper
• Depth gauge or caliper depth rod
• Phillips and flat-head screwdrivers
• Small container for screws
• Phone or camera for reference photos
• Paper or notes app for recording dimensions
• Original upper and lower hinges, when accessible
• Safety glasses and work gloves
• A second person for a large or heavy sash

Safety Warning: Support the sash before loosening or removing a hinge. Once disconnected, the sash may shift, swing, or fall unexpectedly.

Do not place your hands between the sash and frame, and do not rely on the operator alone to support the sash during hinge removal.

A typical four-bar hinge consists of a long mounting track and several interconnected linkage arms. As the sash opens, the linkage pivots and slides along the track.

Common components include:

• Track: Mounts to the window frame.
• Sash arm: Mounts to the operable sash.
• Link arms: Control the sash path and opening geometry.
• Pivots and rivets: Connect the moving bars.
• Slider or shoe: Travels inside the track on some designs.
• Stops or friction features: May limit or control movement.

The phrase “4-bar” refers to the connected linkage system, not necessarily the number of visible mounting pieces or rivets.

Open the window far enough to see the complete hinge assembly. Depending on the window style, the hinges may be mounted along the top and bottom or along the two vertical sides.

Before removal, photograph:

• The complete hinge in the open position
• The frame-track location
• The sash-arm location
• The direction in which the hinge opens
• The position of every mounting screw
• The orientation of the upper and lower hinges
• Any stops, limit devices, or friction adjusters
• Any numbers or manufacturer markings

Mark the installed position of the track and sash arm before removing the hardware.

Record how the window opens when viewed from the interior.

Document:

• Casement, awning, hopper, or projected window style
• Top-, bottom-, left-, or right-side hinge location
• Out-swing or in-swing operation
• Which hinge was installed at the top or bottom
• Which end of the track faced the lock side
• Whether the hinge pair is handed or reversible
• The approximate opening angle

Handing terminology may vary between manufacturers. Compare the physical orientation and movement of the original hinge rather than relying only on a left- or right-hand label.

1. Open the sash to a position that provides access to the screws.
2. Support the sash securely with another person or appropriate support.
3. Mark the track and sash-arm locations.
4. Remove the screws from the sash arm and frame track.
5. Keep the upper- and lower-hinge screws separated and labeled.
6. Lay the hinge on a flat surface for measurement.

If the hinge cannot be removed safely, measure it in place and take clear photos from several angles. In-place measurements may be less precise.

Close or fold the hinge and measure the complete length of the long frame-mounted track.

1. Place the hinge flat on a stable surface.
2. Position the ruler at the farthest end of the track.
3. Measure to the opposite end.
4. Keep the ruler parallel with the track.
5. Record the measurement to the nearest practical fraction or decimal.

The illustrated example shows a track length of approximately 16.72 inches.

Product listings may identify this hinge using a nominal size that is slightly different from the measured overall length. Compare the listed measurement diagram carefully.

Measure across the frame track at a flat, undamaged section. Also measure the sash arm and linkage bars when their width differs from the track.

Record:

• Frame-track width
• Sash-arm width
• Primary linkage-arm width
• Material thickness
• Raised ribs, flanges, or rolled edges
• Slider-channel opening, when present

A replacement that is too wide may not fit the frame pocket, while one that is too narrow may not position or support the sash correctly.

Stack height is the total thickness of the hinge assembly when all of the linkage bars are folded into the closed position.

1. Fold the hinge completely closed.
2. Place it on a flat surface.
3. Use a caliper or depth gauge to measure from the lowest surface to the highest stacked point.
4. Avoid measuring over a raised rivet head unless the product specification includes it.
5. Record the body stack height and any rivet projection separately.

Incorrect stack height may prevent the sash from closing fully, create excessive clearance, or cause the hinge to rub against the frame.

Measure mounting holes from the center of one hole to the center of the next. Record the pattern on both the frame track and sash arm.

Record:

• Center-to-center spacing between adjacent holes
• Spacing between the first and last mounting holes
• Distance from each end of the track to the nearest hole
• Number of holes
• Round or slotted hole shape
• Hole diameter
• Countersunk, raised, or flat mounting surface
• Sash-arm mounting-hole pattern

The example diagram illustrates multiple dimensions because both the complete pattern and the position of individual holes may affect compatibility.

Do not measure from the outside edge of one hole to the outside edge of another.

The sash arm is the portion attached directly to the operable sash. Its length and mounting-hole layout help determine where the hinge supports the sash.

Measure and record:

• Overall sash-arm length
• Sash-arm width and thickness
• Center-to-center mounting-hole spacing
• Distance from the sash-arm end to the first hole
• Shape of the free end
• Any bend, offset, step, or raised section
• Location of the main linkage pivot

Similar frame tracks may be paired with different sash arms, resulting in different opening paths or sash clearances.

The positions and lengths of the interconnected arms determine how the sash moves away from the frame.

Document:

• Length of each primary linkage arm
• Center-to-center distance between pivots
• Location of the sliding pivot or shoe
• Shape and direction of bends
• Offset between overlapping bars
• Number and position of rivets
• Position of any stop or friction adjustment screw

Do not remove rivets or disassemble the linkage for measurement.

Some four-bar hinges are designed to open the sash to a specific angle or move it away from the frame far enough to provide cleaning, ventilation, or emergency-egress clearance.

Observe and record:

• Approximate maximum opening angle
• Distance the hinge side of the sash moves away from the frame
• Clear opening width
• Whether the sash remains near the frame or shifts toward the center
• Presence of a built-in stop or separate limit device
• Whether the hinge includes adjustable friction

Two hinges of the same track length may produce different opening angles or sash positions.

Four-bar hinges may be manufactured from stainless steel, plated steel, or other corrosion-resistant materials.

Record:

• Visible metal type or finish
• Magnetic or non-magnetic response, when useful
• Signs of rust, pitting, or coating failure
• Plastic, nylon, or metal slider material
• Stamped manufacturer name
• Part numbers, patent numbers, or date codes

Match the original corrosion-resistance requirements, especially in coastal, humid, or commercial environments.

Inspect both hinges before ordering. Some window systems use matching hinges, while others use a handed, mirrored, or differently configured upper and lower pair.

Confirm whether they share:

• The same track length
• The same sash-arm length
• The same mounting-hole pattern
• Mirrored linkage orientation
• The same friction or stop features
• The same part number

Replacing hinges as a matched pair can help maintain even sash support when both originals are worn.

Measure each critical dimension at least twice before ordering.

Confirm the following:

• Overall track length
• Track width
• Closed stack height
• Frame-track mounting-hole pattern
• Sash-arm length and mounting holes
• Linkage orientation and pivot spacing
• Upper- and lower-hinge orientation
• Opening angle or projection
• Material and finish
• Manufacturer markings

Small manufacturing tolerances may cause your measurements to differ slightly from a product’s nominal dimensions. Compare the complete hinge design rather than requiring every decimal to match exactly.

Clear photographs can reveal hinge features that are difficult to describe with measurements alone.

Include photos of:

• The complete hinge fully opened
• The complete hinge fully closed
• The side profile showing stack height
• The full frame track
• The full sash arm
• Every mounting hole
• The slider or track shoe
• All linkage pivots and rivets
• Any friction adjuster or stop
• Part numbers and manufacturer markings
• The hinge while still installed
• The complete window from the interior and exterior

Replacement may be appropriate when the hinge no longer supports or guides the sash correctly.

Common signs include:

• Bent linkage arms
• Loose or worn pivot rivets
• A cracked or distorted track
• A damaged slider or shoe
• Heavy corrosion or seized movement
• Excessive sash sag
• The sash rubbing against the frame
• The window no longer closing evenly
• The hinge separating from its mounting surface

Loose mounting screws may sometimes be corrected without replacing the hinge, provided the hinge and mounting material remain undamaged.

• Ordering by track length alone
• Measuring the moving linkage instead of the frame track
• Measuring mounting holes from edge to edge
• Ignoring the sash-arm mounting pattern
• Failing to measure stack height
• Measuring over raised rivets without noting them separately
• Ignoring track and linkage width
• Assuming upper and lower hinges are identical
• Failing to record the hinge orientation
• Ignoring opening angle and sash movement
• Confusing a limit device with part of the hinge
• Discarding the original hardware before testing the replacement
• Removing a hinge without supporting the sash

Before ordering, confirm all of the following:

• Window type and opening direction
• Upper- and lower-hinge orientation
• Overall frame-track length
• Track and linkage widths
• Closed stack height
• Frame-track mounting-hole spacing
• Sash-arm length and mounting pattern
• Linkage-arm lengths and pivot positions
• Slider or shoe configuration
• Maximum opening angle
• Friction, stop, or limit features
• Material, finish, and markings

To identify a replacement 4-bar hinge, measure the complete frame-track length, track width, closed stack height, mounting-hole pattern, sash arm, and linkage geometry.

Also document the window type, hinge orientation, opening angle, material, slider design, and any friction or limit features.

Matching the complete hinge configuration helps the sash open, close, align, and remain supported as intended.