Universal sash lock shims to fix a lock that won’t catch
Most windows that won’t lock aren’t worn out. They’re out of alignment by a hair, sometimes just 1/16 of an inch, from decades of settling, paint layers, and wood movement. That tiny shift is all it takes to make the lock miss its keeper.
Sash lock shims are thin plastic spacers that fit under your sash lock or keeper and raise the hardware just enough to bring it back into line. When the lock engages again, it pulls the meeting rails tight together, which improves both security and the seal at the leakiest part of a double-hung window. Major window manufacturers specify shims as the standard field fix for this, so it’s not a workaround. It’s what restorers use on service calls.
These are our universal shims — a generic 2-3/4″ × 3/4″ size that fits most traditional two-piece sash locks. If you’re running our Solid Brass Sash Lock, grab our PerfectFit Sash Lock Shims instead — they’re cut to that lock’s exact outline and screw pattern so everything lines up with no trimming.
The details
- Material: white opaque plastic that won’t absorb moisture, crack, or show through paint
- Thicknesses: 1/16″ for minor misalignment, 1/8″ for larger gaps
- Dimensions: 2-3/4″ long x 3/4″ wide, matching most traditional sash lock bases
- Mounting: predrilled for standard sash lock screws
- Stackable: combine thicknesses for 3/16″, 1/4″, or more
- Sold individually, in the quantity you need
Which thickness
Close both sashes and look at where the lock meets the keeper. If the step is barely there, start with 1/16″. If there’s an obvious gap between the rails, try 1/8″. When in doubt, buy one of each and test-fit with the screws loose before you commit. It’s easier to remove a layer than to add one after the screws are set.
Where they work
Any wood double-hung window with a traditional two-piece sash lock, from 1850s Greek Revival to 1940s Colonial Revival. They also help on older vinyl and aluminum windows where the meeting rails have shifted. One note: shims fix alignment, not binding. If the sash is sticking from paint buildup, swollen wood, or a failed balance, fix that first.
Frequently asked questions
What are sash lock shims for?
They make a window lock again without replacing anything. Most windows that won’t lock are out of alignment by a hair, sometimes just 1/16 of an inch, from settling, paint layers, and wood movement. The shim fits under your sash lock or keeper and raises the hardware just enough to bring it back into line so the lock catches.
Should I get Universal or PerfectFit shims?
Get Universal if you’re fixing an existing or unknown sash lock — they fit most traditional two-piece locks. Get PerfectFit if you’re using our Solid Brass Sash Lock; they’re cut to that lock’s exact outline and screw pattern so everything lines up with no trimming.
What thicknesses do sash lock shims come in?
Two thicknesses: 1/16 inch for minor misalignment and 1/8 inch for larger gaps. They stack, so you can combine them for 3/16 inch, 1/4 inch, or more.
Which thickness should I use?
Close both sashes and look at where the lock meets the keeper. If the step is barely there, start with 1/16 inch. If there’s an obvious gap between the rails, try 1/8 inch. When in doubt, buy one of each and test-fit with the screws loose before you commit.
What are sash lock shims made of?
White opaque plastic that won’t absorb moisture, crack, or show through paint. They measure 2-3/4 inches long by 3/4 inch wide, matching most traditional sash lock bases, and are predrilled for standard sash lock screws.
Can you buy sash lock shims individually?
Yes. They are sold individually, in the quantity you need, so you buy exactly what your windows need instead of a big pack.