6 Best Steel Shims For Gap Filling Professionals Use

Precision leveling is the silent difference between a structure that settles perfectly and one that develops stress fractures within a year. When metal panels are fastened to an uneven steel purlin or a timber frame has shifted, steel shims act as the bridge that restores structural integrity. Choosing the wrong material leads to compression failure or, worse, accelerated galvanic corrosion that compromises the fasteners themselves. Use this guide to navigate the technical requirements of industrial-grade shimming for your next high-stakes installation.

Disclosure: As an Amazon Associate, this site earns from qualifying purchases. Thank you!

Precision Brand Slotted Shim Kit: Best Overall

This kit earns its reputation by providing a comprehensive range of thicknesses in a single, organized package. Professionals rely on these because they cover the immediate, unpredictable gaps found when installing support brackets on structural steel.

The slotted design allows for quick lateral insertion without removing the bolt entirely. This saves valuable time when adjusting the pitch of solar racking or securing heavy metal flashings where every minute on the ladder counts.

The bottom line: Keep a kit on the truck for general maintenance and unexpected field adjustments. It eliminates the need for guesswork or makeshift fillers.

Maaud Stainless Steel Shims: Best for Coastal Jobs

Coastal environments are notorious for turning standard steel into rust flakes within a few seasons. If you are working within five miles of saltwater, skip carbon steel entirely and spec stainless steel shims to prevent sacrificial corrosion.

These shims maintain their structural thickness over decades, ensuring that the gap between a bracket and a beam doesn’t grow as the material wastes away. They are non-magnetic and highly resistant to the chemical reactions that occur when different metals meet in humid, salty air.

The bottom line: Never compromise on corrosion resistance in coastal zones. Stainless is the only logical choice for long-term structural longevity.

Vulcan Steel Shim Stock: Best for Custom Fitting

Sometimes, the gap doesn’t conform to standard, pre-cut thicknesses. Vulcan shim stock comes in continuous rolls or sheets, allowing the installer to snip the exact shape and thickness required for non-standard mounting points.

This is critical when shimming heavy HVAC equipment on flat roof curbs or aligning uneven steel rafters. Having the ability to cut a custom “spacer” ensures that the load is distributed evenly across the entire surface area of the base plate.

The bottom line: Keep a few rolls in the shop for bespoke installations where standard slotted shims fail to provide full-contact support.

H&R Solid Plate Steel Shims: For Heavy Loads

When dealing with high-stress connections, such as bolting heavy structural steel beams or mounting heavy industrial machinery, solid plate shims are mandatory. Unlike thin, flimsy alternatives, these provide a massive surface area that prevents “caving” under extreme compression.

Their solid, non-slotted design forces a permanent, high-friction connection once the bolt is torqued. They prevent the lateral “walking” that can occur with slotted shims under intense vibration.

The bottom line: Use solid plates for primary structural connections. Save the slotted shims for light-duty alignment and decorative trim work.

WESTWARD Carbon Steel Shims: A Solid Workhorse

Westward shims are the industry standard for interior framing and heavy-duty shop projects where corrosion is not a primary concern. They are rigid, predictable, and hold their shape under significant pressure without deforming.

For interior metal framing or secondary supports where the environment is climate-controlled, these provide the most cost-effective way to bridge gaps. They are easily stackable and integrate well with standard mechanical fasteners.

The bottom line: Reserve these for dry, protected environments. They offer excellent value for the bulk of your structural shimming needs.

Trinity Brand Horseshoe Shims: For Bolt Alignment

Horseshoe shims are the go-to for rapid, efficient alignment of wall panels and base plates. The U-shaped cutout allows them to snap around a bolt that is already tightened, which is perfect for final “tweaks” during a final inspection walkthrough.

They are particularly useful in masonry and heavy timber construction where plumb lines require minor corrections. Their ease of use prevents the frustration of backing out heavy-duty anchors just to insert a spacer.

The bottom line: These are a “time-saver” tool. Keep a box of various thicknesses on hand for final adjustments to panels and bracketry.

Slotted vs. Solid vs. Horseshoe: Pick Your Shim

The shape of the shim dictates how it interacts with the fastener and the structural load. Slotted shims are for speed, horseshoe shims are for fine-tuning, and solid shims are for the ultimate, load-bearing connection.

Never use a horseshoe shim in a high-vibration environment, as the open end can allow the shim to vibrate loose over time. Similarly, don’t use slotted shims for heavy, load-bearing structural columns, as the slot creates a weak point where the shim could potentially buckle.

The bottom line: Match the geometry of the shim to the mechanical requirements of the connection. Speed is good, but structural security is non-negotiable.

Steel vs. Plastic Shims: When to Use Each Type

Plastic shims are convenient for light-duty carpentry, such as door hanging or leveling cabinets, because they don’t rust and can be easily trimmed with a knife. However, they have no place in structural steel or roofing support.

Steel shims provide a constant, unchanging compression rating. Plastics tend to “creep”—they compress and deform under constant, heavy weight—which can cause your carefully leveled structure to sag or shift over time.

The bottom line: If the structure involves steel-on-steel or heavy structural loads, always spec steel. Use plastic only for finish work and non-structural leveling.

How to Safely Stack Shims for Structural Support

Stacking shims is sometimes necessary, but it introduces variables that can compromise a connection. The rule of thumb is to use as few shims as possible; a single thick shim is always superior to a stack of five thin ones.

When you must stack, alternate the orientation of the slots or ensure the entire surface area remains supported. Never create a “pyramid” of shims, as this creates localized pressure points that can snap the fastener or bend the base plate.

The bottom line: Aim for a single-shim solution. If you find yourself stacking more than three shims, rethink your connection or seek a custom-fabricated filler plate.

Stainless vs. Carbon Steel: A Corrosion Guide

The choice between stainless and carbon steel comes down to the environment. Carbon steel is cheaper and stronger in terms of pure tensile force, but it is susceptible to oxidation the moment it is exposed to moisture.

Stainless steel creates an invisible protective film that resists rust, but it is softer and can be more expensive. In any roofing application involving treated lumber, copper flashings, or salt spray, stainless is the only way to avoid a galvanic headache later.

The bottom line: If the shim is exposed to the elements, choose stainless. If it’s buried deep inside a dry structure, carbon steel is perfectly acceptable.

Selecting the right shim is not just about filling a gap; it is about ensuring that the force applied to a fastener is transferred safely through the structure. Whether you are correcting a sag in a purlin or leveling a heavy-duty bracket, the steel you put behind the metal matters as much as the bolt itself. Take the time to match the material and shape to the specific load, and the installation will remain square and secure for years to come.