6 Automotive Body Shims For Leveling Interior Panels

Nothing ruins the aesthetic of a custom cabinetry build or a van interior faster than a cabinet door that hangs crooked or a wall panel that refuses to sit flush. Gaps and misalignments are the inevitable enemies of small-space living, where every surface serves multiple functions and structural integrity is paramount. Mastering the art of the shim is the secret to elevating a DIY project from amateurish to professional-grade.

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Dorman 703-270 Kit: Best Overall Assortment

When starting a project where the exact thickness of the required gap is unknown, the Dorman 703-270 kit serves as the ultimate diagnostic tool. This assortment provides a broad range of plastic shim thicknesses, allowing for immediate trial-and-error adjustment without needing multiple trips to the hardware store.

The plastic construction is ideal for interior panels where wood-on-wood contact might cause squeaking or moisture-related expansion. Because these shims are designed for automotive use, they handle the vibration of a moving vehicle significantly better than makeshift shims cut from scrap material.

This kit is the perfect starting point for any interior build-out. If there is a need for a versatile, “buy it once” solution that covers most standard gap-filling tasks, this is the definitive choice.

Performance Tool W80577: Best Budget Kit

Budget-conscious builders often struggle with the cost of small fasteners and leveling hardware, which can quickly inflate the price of a build. The Performance Tool W80577 kit addresses this by providing a high quantity of shims at a price point that makes it easy to keep a surplus in the toolbox.

While these may lack the premium finish of professional-grade automotive hardware, they perform their primary function—taking up space and ensuring a level fit—perfectly well. They are best suited for non-structural decorative panels or areas where the shims will remain permanently hidden behind trim.

This is the right choice for those tackling large-scale projects who need to distribute shims liberally across multiple cabinets. It is a no-frills, utilitarian solution that delivers value without over-engineering the component.

Auveco 12698 Kit: Pro-Grade Durability

The Auveco 12698 kit is built for those who refuse to compromise on the longevity of their interior installations. These shims are manufactured to tighter tolerances than budget alternatives, ensuring that when an alignment is set, it stays set despite the persistent road vibration found in RVs and campers.

Because these shims are engineered for automotive bodywork, they possess superior compressive strength. They resist deformation under the tension of tightened screws, which is crucial for preventing cabinets from sagging over thousands of miles of travel.

For those building a high-end conversion meant to last for years, this is the gold standard. It is a worthwhile investment for primary structural mounting points where failure or shifting is not an option.

Allstar ALL18204: Best for Precision Work

Precision is the hallmark of a well-executed tiny home interior. The Allstar ALL18204 shims are designed for applications where accuracy is prioritized over sheer quantity, providing consistent, reliable thickness that makes calibrating tight-tolerance panel joints easier.

These shims are particularly useful when mounting heavy fixtures, such as wall-mounted monitors or shelving units, where even a slight tilt becomes magnified over distance. Their standardized dimensions ensure that the leveling process remains predictable throughout the entire assembly.

If the goal is to eliminate the frustration of “close enough” and achieve a perfect, laser-straight finish, reach for this kit. It is the preferred choice for detailed finish work where technical precision takes center stage.

Gardner-Westcott Shims: Best for Bulk Buys

Large renovation projects often require a steady supply of hardware to avoid workflow interruptions. Gardner-Westcott provides a consistent, high-quality bulk solution that ensures the builder never runs out of the right size during the critical phase of hanging cabinetry.

The reliability of these shims lies in their uniformity; there is rarely a variation in thickness between pieces, which simplifies the process of stacking or pairing shims. They are a staple in professional workshops for good reason.

Buy these if the project entails multiple builds or a complete interior overhaul. They offer the best balance of quality and volume for the serious builder who prefers to keep a well-stocked inventory of consumables.

Mr. Gasket 7810G: Best Steel Shims for Strength

When a project demands structural load-bearing support, plastic shims may eventually succumb to cold-flow or deformation. The Mr. Gasket 7810G steel shims provide the incompressible strength required for mounting heavy equipment, metal framing, or engine-adjacent accessories where heat might be a factor.

Steel shims excel in scenarios where a small, thin, but extremely rigid spacer is needed to create a perfectly perpendicular mount. They provide a “hard” connection that, once torqued, will not move or compress under heavy vibration.

Reserve these for critical load-bearing connections or high-heat environments. They are the strongest link in the chain and are essential for any mounting point that carries weight or requires maximum structural rigidity.

Plastic vs. Steel Shims: Which Is Right for You?

The choice between plastic and steel isn’t just about material cost; it’s about the physics of the installation. Plastic shims are generally superior for non-structural, interior applications because they are naturally vibration-dampening, non-conductive, and immune to rust. They are the ideal choice for cabinetry, trim, and wall panels.

Steel shims are reserved for structural integrity and high-torque environments. If a component bears weight or acts as a structural anchor, steel provides a permanent, non-compressible interface. However, steel shims can transfer vibration and potentially lead to rattles if not properly tensioned against a soft gasket.

Consider the environment before choosing. If the area is prone to moisture or condensation, avoid steel to prevent hidden corrosion. For interior aesthetics and ease of adjustment, plastic remains the versatile champion of the tiny living space.

How to Perfectly Shim an RV Cabinet or Panel

Proper shimming starts with a level, not just the cabinet. Use a quality torpedo level to find the high and low points of the wall or frame. Once the irregularities are mapped, mark the location of every mounting hole.

Place the shim over the fastener location and press it firmly against the wall. Before tightening the final screw, verify the alignment with a square; even a perfectly level cabinet will look wrong if it isn’t square to the surrounding panels.

Do not over-tighten screws to “force” a fit. If the gap is too large, use a thicker shim or stack shims until the fastener can be tightened without distorting the cabinet face. A shimmed connection should feel solid and secure, not under tension from a bent cabinet wall.

Beyond Panels: Other Smart Shim Uses in Your Rig

Shims serve as more than just gap-fillers for walls. They are essential for leveling heavy appliances like refrigerators, which require a level base for proper cooling unit operation. A shimmed-up fridge ensures the internal door seals function correctly and prevents mechanical strain.

Use shims to level drawer slides inside custom-built cabinetry. If the slide is even a fraction of an inch out of alignment, the drawer will either creep open while driving or stick when trying to open it.

Additionally, use shims to provide clearance for cable routing behind wall panels. Creating a small gap with a shim allows for clean, hidden electrical runs without needing to notch expensive structural framing members.

Shim Stacking and Trimming for a Clean Fit

While stacking shims is sometimes necessary, it should be done with care. Limit stacking to two or three shims maximum to maintain structural stability. If more height is required, consider using a solid wood block or a single piece of dense material to bridge the gap.

If a shim extends past the edge of the panel after installation, trim it back using a sharp utility knife or a flush-cut saw. A clean, invisible shim is the mark of professional craftsmanship.

Always check for “shim creep” during the first few test drives. If shims move, add a small dab of construction adhesive between them or use a washer to lock them in place. A properly shimmed panel should remain silent and perfectly placed for years of travel.

Mastering the use of shims is a rite of passage for any builder working in mobile, compact spaces. By choosing the right material for the task and applying them with patience, the result will be a beautiful, rattle-free, and perfectly square interior.