What is a sash lock and how does it work?

A sash lock (also called a cam lock or sash cam) is the latch mechanism mounted on the upper rail of the lower sash of a double-hung window. When you rotate the handle, a curved cam on the underside of the lock engages with a keeper (strike plate) mounted on the lower rail of the upper sash. The cam pulls the two sashes together and prevents them from being raised. A working sash lock is essential for both security and weathertightness — a locked sash pulls the window sashes into firm contact with each other and the weatherstripping.

How do I know if I need a new lock or just an adjustment?

Test the lock carefully: (1) Does the handle turn fully but not pull the sashes together? The keeper may be misaligned or the cam is worn. Try loosening the keeper screws and repositioning it so the cam engages fully. (2) Does the handle spin freely without resistance? The cam mechanism inside the lock housing is broken. Replace the lock. (3) Does the handle not turn at all? The lock is frozen from paint or corrosion. Score around the lock housing with a utility knife to cut through paint, then try again. If still stuck, replace the lock. (4) Does the handle turn but the window still slides open? The cam is not reaching the keeper. The keeper needs to move closer to the cam, or the lock needs to be replaced with a taller cam profile.

Are window sash locks universal or do I need a specific replacement?

Most double-hung window sash locks are standardized and interchangeable, but there are variations in: (1) the screw hole spacing (most common is 1-3/4 inch center to center, but some are 2-1/4 inch); (2) the cam height (the distance the cam extends — a taller cam compensates for gaps between sashes); and (3) the finish (white, brass, chrome, bronze). Before buying a replacement, measure the screw hole spacing on your existing lock. Bring the old lock to the hardware store or match the model number if it is printed on the lock body.

Can a window lock be picked or bypassed easily?

Standard sash cam locks provide modest security — they resist casual opening but a determined intruder can bypass them. For first-floor windows or windows in concealed locations, supplement the sash lock with a window pin lock (a bolt that pins the two sashes together through drilled holes), a window bar, or a keyed window lock. Keyed sash locks require a key to open from the inside as well, which adds significant security but means you need the key to open the window from inside — consider egress requirements before installing keyed locks on bedroom windows.

How do I remove a sash lock that has been painted over?

Painted-over sash locks are common in older homes that have had multiple paint jobs. Use a sharp utility knife to score around the entire perimeter of the lock housing, cutting through the paint film at the seam between the lock and the window rail. Score around each screw head as well. Try to turn the screws — they should now break free of the paint. If the screws are still stuck, use a screw extractor or a manual impact driver. Once the lock is off, scrape the paint residue from the mounting surface and clean it flat before installing the new lock.

My replacement lock does not line up with the existing screw holes. What do I do?

If the new lock has a different screw hole spacing than the old one: (1) fill the old screw holes with wood filler or a wooden toothpick dipped in wood glue pressed into the hole; let cure fully. (2) Mark and drill new pilot holes at the correct spacing for the new lock. (3) Drive screws into the new holes. Do not try to drive new screws into the edge of old holes — the screw will wander and the lock will not mount securely. Filling and redrilling takes only a few minutes and gives a solid mount.

How to Fix a Broken Window Lock: Step-by-Step Guide

A broken window lock is a security vulnerability and a weatherproofing problem.

A broken window lock is a security vulnerability and a weatherproofing problem. Most double-hung window sash locks are inexpensive parts that take about 30 minutes to swap out, even for a first-time repair.

What You Need

Replacement sash cam lock (measure your screw hole spacing first) — match the screw hole spacing and finish of the original
Window sash keeper/strike plate — replace the keeper if it is damaged or if you are upgrading the lock
Phillips-head screwdriver
Utility knife
Measuring tape (to measure existing screw hole spacing)
Wood filler (if relocating screw holes)
Power drill with small pilot bit

Step 1: Identify the Problem

Before ordering a replacement, confirm the lock itself is the problem and not a simple alignment issue.

Check the keeper alignment. Close both sashes fully. Does the cam on the lock body line up with the center of the keeper? If the keeper is too high or too low, the cam cannot engage fully. Loosen the keeper screws and slide the keeper up or down by 1/8 inch increments until the cam snaps in firmly when you turn the handle. Retighten. If this resolves the problem, you do not need a new lock.

Check for paint binding. On older windows, multiple layers of paint can prevent the lock handle from rotating. Score around the lock housing with a utility knife and try the handle again.

Check the cam. If the handle turns but nothing engages the keeper, the cam inside the lock housing is broken or worn. The lock needs replacement.

Step 2: Remove the Old Lock

Close the lower sash fully so the mounting surface is accessible. Use a utility knife to score around the perimeter of the lock body, breaking through any paint that has sealed it to the window rail. Score around each screw head as well.

Remove both mounting screws with a Phillips screwdriver. If the screws spin without loosening (stripped), use a screw extractor set to remove them. Lift the lock body straight off the rail — it should come free cleanly. If it is stuck from paint or caulk, work a stiff putty knife under the edge to break the seal.

Examine the mounting surface. If the old screw holes are enlarged or damaged, fill them with wood filler. Let cure completely before drilling new pilot holes.

Step 3: Remove the Old Keeper

The keeper (strike plate) is mounted on the lower rail of the upper sash. Open the lower sash slightly to access the keeper. Score around it with a utility knife and remove the mounting screws.

If the keeper is in good condition and properly positioned for the new lock, you may be able to reuse it. If you are installing a lock with a different cam height or geometry, replace the keeper with the matching keeper that came with the new lock.

Step 4: Install the New Lock

Measure and mark screw holes. If the new lock has the same screw hole spacing as the old one and the holes are in good condition, you can drive screws directly into the existing holes. If not, use the new lock as a template: position it where you want it on the rail, mark through the screw holes with a pencil, and drill small pilot holes at each mark.

Mount the lock body. Place the new lock on the upper rail of the lower sash, aligning the screw holes. Drive both screws snugly — firm but not over-tightened. Over-tightening can crack the lock housing or strip the holes in the wood rail.

Step 5: Install and Align the Keeper

With the lower sash closed and the new lock in place, turn the lock handle to the locked position. The cam will protrude downward toward the upper sash. Hold the new keeper against the lower rail of the upper sash at the point where the cam makes contact. Mark the screw hole locations and drill pilot holes.

Mount the keeper with its screws, but do not fully tighten yet. Test the lock: close both sashes, turn the handle to lock, and check that the cam engages the keeper smoothly and pulls the sashes firmly together. Adjust the keeper position up or down as needed, then fully tighten.

Step 6: Test Security and Operation

Lock and unlock the window five times to confirm smooth operation. Pull up on the lower sash while locked — there should be no movement. Check that the sashes are pulled snugly together by the locked cam; you should not be able to see daylight between the sash rails when locked.

If the lock is stiff, rub a little paste wax on the cam. Do not use liquid lubricants — they attract dust and eventually gum up the mechanism.

How to Fix a Stuck Window — freeing painted-shut or warped double-hung windows
How to Weatherstrip a Window — sealing drafts around windows for energy efficiency
How to Replace a Window Screen — re-screening a torn or damaged window screen frame

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Identify the Problem
Before ordering a replacement, confirm the lock itself is the problem and not a simple alignment issue.
Remove the Old Lock
Close the lower sash fully so the mounting surface is accessible. Use a utility knife to score around the perimeter of the lock body, breaking through any paint that has sealed it to the window rail. Score around each screw head as well.
Remove the Old Keeper
The keeper (strike plate) is mounted on the lower rail of the upper sash. Open the lower sash slightly to access the keeper. Score around it with a utility knife and remove the mounting screws.
Install the New Lock
Measure and mark screw holes. If the new lock has the same screw hole spacing as the old one and the holes are in good condition, you can drive screws directly into the existing holes.
Install and Align the Keeper
With the lower sash closed and the new lock in place, turn the lock handle to the locked position. The cam will protrude downward toward the upper sash.
Test Security and Operation
Lock and unlock the window five times to confirm smooth operation. Pull up on the lower sash while locked — there should be no movement.

How to Fix a Broken Window Lock: Step-by-Step Guide

What You Need

Step 1: Identify the Problem

Step 2: Remove the Old Lock

Step 3: Remove the Old Keeper

Step 4: Install the New Lock

Step 5: Install and Align the Keeper

Step 6: Test Security and Operation

Free: 10-Point Home Maintenance Checklist

Save this for next time.

How to Fix a Broken Window Lock: Step-by-Step Guide

What You Need

Step 1: Identify the Problem

Step 2: Remove the Old Lock

Step 3: Remove the Old Keeper

Step 4: Install the New Lock

Step 5: Install and Align the Keeper

Step 6: Test Security and Operation

Related Reading

Free: 10-Point Home Maintenance Checklist

Save this for next time.