Choose a GlazeLock Shim by Shape, Slot, Size and Material

By Kevin Cody | Founder & CEO, FLI Products / Mary Joan Isorena, Communications
Published: September 29, 2026

GlazeLock shims come in different shapes, sizes, thicknesses and materials because installation gaps and leveling requirements are not all the same. This guide explains how horseshoe, interlocking, snap-off, flat plate, tapered and wood shims differ—and what to consider when choosing the right GlazeLock shim for your project.

Glazelock, a partner brand, sold by FLI Products.

For more GlazeLock shim guides and product resources, visit the GlazeLock Hub.

Key Takeaways

• GlazeLock offers several shim profiles, including U-shaped/horseshoe, interlocking, snap-off stackable, flat plate, tapered plastic and natural pine designs.

• Choosing the right shim starts with the required shape and available installation space, not thickness alone.

• U-shaped GlazeLock shims are available in different overall dimensions and slot widths, including 1/2", 5/8" and 7/8" configurations, depending on the product.

• Interlocking and snap-off/stackable are different product designs. Not every GlazeLock horseshoe shim is interlocking.

• Flat plate shims provide a solid rectangular spacing surface, while tapered wedges provide progressive adjustment along their length.

• GlazeLock includes both plastic and natural pine shim options.

• Dimensions, thicknesses, materials and package configurations vary by product, so check the individual product page before ordering.

Why Shim Design Matters

A shim may be a small part of an installation, but choosing one starts with understanding the space that needs to be adjusted.

The required shape, thickness, overall dimensions, slot size and material can vary according to the installation. A U-shaped shim, for example, has a very different profile from a tapered wedge. A compact horseshoe shim is designed for a different physical space than a larger 4" × 3" horseshoe shim.

That is why GlazeLock is not a single-shim system.

The GlazeLock range includes multiple configurations for leveling, spacing and alignment work, with products for applications including windows, doors, cabinets, glazing and general construction.

Instead of asking only, “What thickness shim do I need?”, start with a broader question:

What shape, size and adjustment method does the installation require?

GlazeLock Shim Types at a Glance

Several GlazeLock formats are available, each with its own dimensions, profile and design.

Because dimensions, thicknesses and package configurations vary by product, check the individual product page before ordering for a specific installation.

1. Compact U-Shaped Horseshoe Shims

GlazeLock Compact U-Shaped Horseshoe Shims measure 2" × 1-1/2" and have a 1/2" slot.

Available thicknesses include 1/16", 1/8" and 1/4". They are made from durable plastic and are available in red, blue and black for thickness identification.

Their defining characteristic is their compact size. The 2" × 1-1/2" format is suited to tighter spaces where a larger shim may not fit.

The open U-shaped design allows the shim to fit around compatible hardware rather than requiring a solid plate to occupy the same space.

Key specifications:

• Dimensions: 2" × 1-1/2"

• Slot: 1/2"

• Shape: U-shaped / horseshoe

• Material: Durable plastic

• Colors: Red, blue and black

• Thickness options: 1/16", 1/8" and 1/4"

• Made in USA

Best reason to consider this format: The installation requires a smaller horseshoe shim for the available space.

Shop GlazeLock Compact U-Shaped Horseshoe Shims

2. Interlocking U-Shaped Shims

GlazeLock Interlocking U-Shaped Shims measure 3" × 1-1/2" with a 1/2" slot.

Unlike a standard horseshoe profile defined primarily by its shape and dimensions, this model incorporates an interlocking design. The shims lock together when stacked, helping prevent shifting while allowing multiple shims to be combined for the required spacing.

Available thicknesses include 1/16", 1/8" and 1/4".

Key specifications:

• Dimensions: 3" × 1-1/2"

• Slot: 1/2"

• Shape: U-shaped / horseshoe

• Design: Interlocking

• Material: High-impact plastic

• Thickness options: 1/16", 1/8" and 1/4"

• Assorted colors

• Made in USA since 1997

Best reason to consider this format: The installation calls for a U-shaped shim and an interlocking connection when multiple shims are stacked.

Shop GlazeLock Interlocking U-Shaped Shims

3. Extended U-Shaped Horseshoe Shims

Sometimes the basic shape is right, but the required dimensions are different.

GlazeLock Extended U-Shaped Horseshoe Shims measure 3-1/2" × 1-1/2" and retain a 1/2" slot.

This provides another horseshoe-size option between GlazeLock's smaller formats and its larger 4" × 3" products.

Several thickness and package configurations are available, so check the individual product page for the exact option needed for your project.

Key specifications:

• Dimensions: 3-1/2" × 1-1/2"

• Slot: 1/2"

• Shape: U-shaped / horseshoe

• Made in USA

Best reason to consider this format: A longer U-shaped shim is required while retaining the 1/2" slot configuration.

Shop GlazeLock Extended U-Shaped Horseshoe Shims

4. Snap-Off Stackable Horseshoe Shims

GlazeLock also offers snap-off stackable horseshoe shim designs.

The Green Snap-Off Stackable Horseshoe Shim measures 4-3/16" × 1-7/8" and has a 5/8" slot.

This model combines snap-off sections with a stackable design, distinguishing it from GlazeLock's interlocking U-shaped models.

The green version is made from high-impact polystyrene and is available in 1/32" and 1/16" thicknesses.

Key specifications:

• Dimensions: 4-3/16" × 1-7/8"

• Slot: 5/8"

• Shape: Horseshoe / U-shaped

• Design: Snap-off sections and stackable

• Material: High-impact polystyrene

• Color: Green

• Thickness options: 1/32" and 1/16"

• Made in USA

Best reason to consider this format: The installation benefits from a stackable horseshoe shim with a snap-off design.

Shop GlazeLock Green Snap-Off Stackable Horseshoe Shims

Additional 1-7/8"-wide Snap-Off Stackable Horseshoe Shims are available in different length and package configurations.

5. Heavy-Duty and Larger Horseshoe Formats

Not every installation requires the same footprint or slot size.

GlazeLock's larger horseshoe options include 4" × 3" models with a 7/8" slot.

The GlazeLock Heavy-Duty Interlocking U Shim combines these larger dimensions with an interlocking design that allows the shims to lock together when stacked.

The GlazeLock Square Horseshoe Shim also measures 4" × 3" with a 7/8" slot.

That distinction is important: two shims can have similar overall dimensions while differing in their exact product design.

When comparing larger GlazeLock horseshoe shims, consider:

• Overall dimensions

• Slot width

• Thickness

• Whether the specific model is interlocking

• Material

• Package quantity

• Requirements of the installation

6. Flat Plate Shims

Not every adjustment requires an open U-shaped profile.

GlazeLock Flat Plate Shims use a rectangular flat-plate design for applications including window and door installation, cabinet leveling and general construction spacing.

Available thicknesses include 1/16", 1/8" and 1/4".

Different colors help identify thicknesses, making it easier to distinguish shim sizes during selection and installation.

Key specifications:

• Shape: Rectangular flat plate

• Material: Durable plastic

• Thickness options: 1/16", 1/8" and 1/4"

• Multiple colors for thickness identification

• Made in USA since 1997

Best reason to consider this format: The installation requires a flat rectangular spacing or leveling surface rather than an open horseshoe profile.

Shop GlazeLock Flat Plate Shims

7. Wedgelock Plastic Shims

Horseshoe and flat shims provide predetermined thicknesses. A tapered wedge works differently.

The GlazeLock WL02 Wedgelock Shim measures 8" × 1-1/2" × 5/16" and uses a tapered wedge profile.

It is made from black plastic and is available in a 288-piece box.

The WL02 is designed for applications including window, door, cabinet and general construction leveling and spacing.

Because the shim is tapered, adjustment is made through the position of the wedge rather than only by selecting and stacking flat shim thicknesses.

Key specifications:

• Dimensions: 8" × 1-1/2" × 5/16"

• Model: WL02

• Shape: Tapered wedge

• Material: Black plastic

• Quantity: 288 per box

• Made in USA

Shop GlazeLock Wedgelock Shims

8. GL-H8 Tapered Wedge Shims

The GlazeLock GL-H8 provides another tapered plastic option.

It measures 1-1/2" × 7-3/4" and is made from black plastic.

The GL-H8 is designed for applications including window and door installation, cabinet alignment, and general construction leveling and spacing.

Like the Wedgelock, its tapered profile allows the amount of adjustment to change as the shim is positioned farther into or out of the gap.

Key specifications:

• Dimensions: 1-1/2" × 7-3/4"

• Model: GL-H8

• Shape: Tapered wedge

• Material: Black plastic

• Made in USA since 1997

Shop GlazeLock GL-H8 Tapered Wedge Shims

9. Natural Pine Wood Shims

GlazeLock is not limited to plastic shims.

GlazeLock Natural Pine Wood Shims provide a traditional tapered wood option measuring 8" × 1-1/4" × 3/8".

Both Original and Prescored versions are available.

These natural pine shims are designed for window, door and cabinet installation as well as general construction leveling.

Rather than treating plastic and wood as interchangeable products, consider the material, shape and requirements of the installation before choosing between them.

Key specifications:

• Material: Natural pine

• Shape: Tapered wedge

• Dimensions: 8" × 1-1/4" × 3/8"

• Versions: Original and Prescored

• Made in USA

Shop GlazeLock Natural Pine Wood Shims

How to Choose the Right GlazeLock Shim

With several formats available, choosing a shim becomes easier when you evaluate the installation in a consistent order.

1. Start With the Required Shape

First determine whether the installation calls for a horseshoe/U-shaped shim, flat plate or tapered wedge.

A horseshoe shim provides an open slot.

A flat plate provides a solid rectangular contact surface.

A tapered wedge provides progressive adjustment along its length.

Do not select a shim based on thickness alone if its physical shape does not suit the installation.

2. Measure the Available Space

Check the length and width available for the shim.

GlazeLock horseshoe designs range from compact formats such as 2" × 1-1/2" to larger 4" × 3" models.

Those dimensions are not interchangeable simply because both products are horseshoe shims.

3. Check the Slot Size

For U-shaped designs, slot width is another important dimension.

Current GlazeLock examples include:

• 1/2" slots on several compact, interlocking and extended U-shaped models

• 5/8" slot on the green snap-off stackable model

• 7/8" slots on larger 4" × 3" horseshoe models

Verify that the slot dimensions are appropriate for the installation and any compatible hardware involved.

4. Determine the Thickness Needed

Once the basic shape and dimensions are established, determine the amount of spacing or adjustment required.

Some GlazeLock flat and U-shaped products are available in predetermined thicknesses. Stackable designs allow multiple pieces to be combined where appropriate.

Tapered wedges work differently because the effective adjustment changes according to how far the wedge is inserted.

Always work from actual measurements and the requirements of the installation.

5. Understand the Product Design

Do not assume all GlazeLock shims work the same way.

Depending on the specific product, the design may be:

• Standard horseshoe

• Interlocking

• Snap-off and stackable

• Flat plate

• Tapered plastic wedge

• Tapered natural pine

Those differences are an important part of selecting the appropriate shim.

6. Verify the Material

The GlazeLock range includes several plastic constructions as well as natural pine.

For example, the 3" interlocking U-shaped shim is made from high-impact plastic, while the green snap-off shim is made from high-impact polystyrene and the wood shim is made from natural pine.

Check the individual product rather than assuming one material specification applies to the entire GlazeLock line.

7. Check the Exact Product Before Ordering

Thicknesses, package quantities and configurations differ among GlazeLock products and variants.

Check the individual product page for:

• Dimensions

• Thickness

• Slot size

• Material

• Package quantity

• Current product configuration

• Availability

Horseshoe vs. Flat vs. Tapered Shims: What's the Difference?

One of the easiest ways to understand the GlazeLock range is by comparing its three fundamental profiles.

Horseshoe / U-Shaped Shims

These have an open slot and are available in several dimensions and slot widths. Some GlazeLock horseshoe models also incorporate interlocking or snap-off/stackable designs.

Flat Plate Shims

These provide a rectangular, non-tapered surface and are available in predetermined thicknesses.

Tapered Wedge Shims

These become progressively thicker along their length. GlazeLock offers both plastic tapered wedges and traditional natural pine wedge shims.

There is no single GlazeLock format that automatically replaces the others. The appropriate design depends on the physical requirements of the installation.

Installing Windows or Doors?

Choosing the shim is only one part of the installation process.

For more detailed application guidance, see:

How to Shim a Window for a Perfect Fit

How to Shim a Door Frame the Right Way

You can also learn more about the development of the GlazeLock product line in:

GlazeLock Shims: The Installer-Driven Innovation Changing Window & Door Installation

Find the GlazeLock Shim That Fits Your Installation

A shim should not be selected simply because its general shape looks similar to one used on another project.

Start with the installation. Determine the required shape, measure the available space, check the slot dimensions where applicable, determine the necessary adjustment, and then compare the appropriate GlazeLock configurations.

Explore GlazeLock horseshoe, interlocking, snap-off, flat plate, tapered plastic and natural pine shim options in multiple dimensions and package configurations.

Shop the GlazeLock Collection

A partner brand, sold by FLI Products.

Frequently Asked Questions

What types of shims does GlazeLock offer?

The GlazeLock range includes U-shaped/horseshoe shims, interlocking U-shaped designs, snap-off stackable horseshoe shims, flat plate shims, tapered plastic wedges and natural pine wood shims. Dimensions and configurations vary by product.

What is a horseshoe shim?

A horseshoe shim is a flat shim with an open U-shaped slot. GlazeLock offers several horseshoe dimensions and slot widths, including compact, extended, interlocking, snap-off and larger square formats.

What is the difference between a horseshoe shim and a wedge shim?

A horseshoe shim has a flat profile of a predetermined thickness with an open slot. A tapered wedge becomes progressively thicker along its length, allowing the amount of adjustment to change according to its position in the gap.

Are all GlazeLock shims interlocking?

No. Interlocking is a feature of specific GlazeLock products, including the 3" × 1-1/2" Interlocking U-Shaped Shims and the 4" × 3" Heavy-Duty Interlocking U Shims.

Other GlazeLock products use different designs, including standard horseshoe, snap-off/stackable, flat plate and tapered wedge configurations.

What is a snap-off stackable shim?

GlazeLock snap-off stackable shims combine sections designed to snap off with the ability to stack multiple shims.

Available configurations include a green 4-3/16" × 1-7/8" horseshoe model with a 5/8" slot.

What thicknesses are GlazeLock shims available in?

Thickness depends on the specific product.

For example, the 3" × 1-1/2" interlocking U-shaped shim is available in 1/16", 1/8" and 1/4" thicknesses, while the green snap-off stackable model is available in 1/32" and 1/16" thicknesses.

Check the individual product page for the exact options available.

Why are some GlazeLock shims different colors?

Color coding helps distinguish thicknesses on several GlazeLock plastic shim products. Because configurations vary, check the individual product page for the colors and thicknesses available for a specific model.

Does GlazeLock make wood shims?

Yes. GlazeLock Natural Pine Wood Shims measure 8" × 1-1/4" × 3/8" and are available in Original and Prescored versions.

Are GlazeLock shims Made in the USA?

Yes. The GlazeLock products covered in this guide are identified as Made in USA.

Where can I buy GlazeLock shims?

GlazeLock shims are available from FLI Products. Visit the complete GlazeLock collection to compare current products, dimensions, package quantities and availability.

Shop All GlazeLock Shims

About Kevin Cody

Kevin Cody | Founder & CEO, FLI Products

Kevin Cody is the Founder and CEO of FLI Products and a product development, merchandising and retail industry veteran with more than 20 years of experience. His background includes merchandising leadership at The Home Depot as well as developing, sourcing, manufacturing, marketing and bringing consumer products to market through major retailers and online marketplaces.

Kevin works directly with manufacturers, inventors, retailers and consumers to develop practical products that solve everyday problems. His experience spans product design and development, retail merchandising, manufacturing, e-commerce, marketplace strategy and consumer product education.

Through the FLI Products Learning Center, Kevin shares practical, experience-based information designed to help consumers better understand products, solve problems and make informed purchasing decisions.

Read Full Bio

About FLI Products

FLI Products develops and markets practical consumer products designed to solve everyday problems at home, outdoors and on the job. Working directly with manufacturers, inventors and retailers, FLI Products focuses on thoughtful product design, practical functionality and useful solutions for consumers. Its products are available through FLIProducts.com and select major retailers and online marketplaces.

About FLI Products

For more GlazeLock shim guides and product resources, visit the GlazeLock Hub.