6 Best Hardened Steel Shims For Leveling Connections

Leveling structural connections is the difference between a roof that sheds water perfectly and one that develops standing pools. When metal-to-metal or metal-to-concrete gaps emerge due to settling or structural tolerances, standard shims often crush or shift under load. Hardened steel shims provide the incompressible foundation necessary to maintain structural integrity across heavy-duty framing and roofing support systems. Selecting the right shim ensures that load paths remain direct, preventing the fastener fatigue that leads to long-term failure.

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Precision Brand Slotted Shims: Best All-Purpose

Precision Brand slotted shims serve as the industry standard for general machinery and structural leveling. The U-shaped slot design allows for quick installation around existing bolts without needing to fully back them out.

These shims excel in scenarios where quick micro-adjustments are required, such as aligning base plates for metal roof support columns. Because they are manufactured from high-quality carbon steel, they resist “mushing” when torque is applied to the fastener.

Bottom line: Choose these for routine jobs where speed and consistent thickness are the primary goals. Avoid them if the application involves high-frequency vibration or extreme corrosive exposure, as they lack the finish of specialized alternatives.

McMaster-Carr High-Strength Shims: Pro’s Choice

McMaster-Carr remains the go-to for professionals who require specific material grades and exact tolerances. Their shim stock offers a level of uniformity that off-the-shelf hardware store alternatives often fail to match.

For high-stakes connections, such as bolting heavy-duty purlins to structural steel, these shims provide predictable compressive strength. The ability to source exact thicknesses ensures that load-bearing joints remain perfectly plumb and level.

Bottom line: Use these when the project specifications demand verified material properties or extreme precision. They represent the best value for contractors who cannot afford a “trial and error” approach to leveling.

Dayton Superior Horseshoe Shims: For Rebar & Bolts

Dayton Superior horseshoe shims are engineered specifically for the construction and concrete trades. Their unique shape and sturdy construction make them ideal for heavy structural connections involving anchor bolts and rebar cages.

These shims hold up under the immense pressure of structural steel beams being set onto concrete foundations. Unlike thinner general-purpose shims, these are designed to maintain their shape under extreme, localized vertical loads.

Bottom line: Keep a supply of these on hand for foundation leveling and heavy steel-to-concrete connections. Their structural rigidity far exceeds that of stamped sheet metal shims when under heavy compression.

G-Shim Hardened Leveling Shims: For Heavy Loads

G-Shim offers hardened options that are explicitly rated for heavy structural support. Where other shims might deflect or deform under the weight of massive metal assemblies, these maintain their geometry.

These are essential when dealing with long-span metal roofs where deflection at the support point would compromise the entire assembly. By providing a solid, incompressible interface, they prevent the fasteners from becoming the primary load-bearing points.

Bottom line: Opt for these in heavy-duty commercial builds where safety factors are critical. They are an insurance policy against structural movement and bolt shear over time.

Starrett 666 Feeler Stock: For Precision Gaps

Starrett is synonymous with precision measurement, and their shim stock is designed for when the gap is razor-thin. When leveling a precision connection where standard structural shims are too thick, feeler stock offers the necessary resolution.

Using these is a common practice when installing concealed fastener systems that require a perfectly flat surface for the clips to engage. Even a 0.005-inch discrepancy can prevent a clip from locking properly, leading to uplift vulnerability during high-wind events.

Bottom line: Keep a set for fine-tuning joints that require absolute mechanical accuracy. They are not intended for heavy structural support but are unmatched for gap-filling in tight-tolerance assemblies.

Lehigh-Armstrong Color-Coded Shims: For Fast ID

Efficiency on the job site is often determined by the ability to identify components quickly. Lehigh-Armstrong color-coded shims remove the guesswork from the leveling process by assigning a specific color to each thickness.

This prevents the common mistake of grabbing the wrong gauge while working on a ladder or in a dark attic space. For roofing contractors managing multiple crew members, this system reduces errors in shim selection during the critical installation of roof curbs or HVAC support stands.

Bottom line: Invest in a color-coded system to improve speed and reduce installation errors. It is a simple administrative win that pays for itself in labor hours saved.

Hardened Steel vs. Stainless vs. Plastic Shims

The choice of material determines how long a connection will remain level. Hardened steel offers the highest compressive strength, making it the only choice for primary structural load paths.

Stainless steel shims should be reserved for high-moisture environments or when working with aluminum components to prevent galvanic corrosion. Plastic shims, while inexpensive and rot-resistant, are generally unsuitable for structural connections because they suffer from “creep,” or slow deformation under constant load.

• Hardened Steel: High strength, requires anti-corrosion coating.
• Stainless Steel: Corrosion resistant, ideal for coastal roofs.
• Plastic: Non-conductive, best for non-structural, light-duty spacers.

Bottom line: Use hardened steel for structure, stainless for corrosion resistance, and avoid plastic for anything that bears significant weight.

How to Correctly Size and Stack Your Steel Shims

Correct leveling is not just about placing a shim; it is about proper stack management. When stacking steel shims, place the thickest shims at the bottom and the thinnest at the top.

Avoid creating “shim towers” by stacking too many individual layers, as this introduces instability and potential for slippage. If a gap exceeds a quarter-inch, it is usually better to use a single, thicker plate or to adjust the steelwork rather than creating a dangerously tall stack.

Bottom line: Limit stacks to three shims maximum to ensure the connection remains solid. If the gap requires more, investigate whether a structural grouting solution is required instead.

Understanding Shim Load & Compressive Strength

Every structural connection has a design load, and the shims supporting that load must meet or exceed it. Hardened steel shims are effective because they do not compress; however, they can create point-load issues if they do not cover the entire mating surface of the plate.

Ensure the shim surface area is sufficient to distribute the weight across the intended bearing surface. Inadequate surface contact leads to the fastener pulling the metal plate toward the shim, creating a bow that weakens the entire joint.

Bottom line: Match the shim size to the footprint of the connection. If the shim is significantly smaller than the contact surface, it becomes a point of weakness rather than a point of support.

Preventing Corrosion on Your Structural Steel Shims

Even the most robust steel shims will fail if they rust away at the base of a structural connection. Before installation, ensure all carbon steel shims are properly coated with a cold-galvanizing spray or a high-quality zinc-rich primer.

In roofing applications, where condensation often migrates to the coldest part of the steel support, this step is non-negotiable. Trapped moisture between a shim and a base plate will cause “pack rust,” which eventually expands and forces the joint open, compromising the connection.

Bottom line: Treat every shim as a potential corrosion point. If the budget allows, use galvanized or stainless options to permanently eliminate the risk of structural degradation.

Selecting the right shim is a matter of matching material performance to the demands of the structural connection. By prioritizing incompressible materials and proper installation techniques, contractors ensure the long-term stability and safety of the roof structure. Always verify local code requirements regarding structural adjustments before finalizing any leveling work on load-bearing components.