Best Notched Shims in 2026

Material Composition and Durability

The primary decision factor for any notched shim is the base material. Because molds often operate under extreme heat and high pressure, you must match the shim's thermal expansion coefficient to the mold plates themselves. Stainless steel shims are the industry standard for corrosion resistance and durability, especially in environments where cooling fluids or moisture are present. However, for high-precision applications requiring minimal deformation under load, hardened tool steel or specialized alloys are preferred. If your application involves high-temperature injection molding, ensure the material won't oxidize or lose its structural integrity at operating temperatures, as this can lead to uneven mold closure and flashing.

Notch Geometry and Precision

The 'notch' is the defining feature of these components, and its design dictates how the shim will behave under load. You must evaluate the depth, width, and angle of the notches. Deep notches are often used to allow for fluid bypass or to accommodate specific protrusions in the mold assembly, while shallow notches are better for providing incremental height adjustments. Precision is paramount here. Look for shims with clean, deburred edges. Any burr or irregularity in the notch can create a stress concentrator, leading to premature cracking or, worse, an uneven surface that compromises the mold's seal. Ensure the notch profile matches the specific geometry of your mold's mating surface to prevent point-loading.

Thickness Tolerance and Uniformity

In mold making, 'close enough' is rarely sufficient. When selecting notched shims, you must look for tight thickness tolerances. A shim that varies in thickness across its surface will introduce tilt or misalignment into the mold cavity. High-quality shims should be specified with micron-level tolerances. When reviewing options, check if the manufacturer provides a tolerance rating (e.g., +/- 0.001mm). This is especially critical if the shim is being used to correct a taper or to manage a specific gap between two heavy mold halves.

Load Distribution and Mechanical Stability

Consider how the shim will distribute the clamping force of the press. A notched shim is often used to create a specific pressure profile. If the notches are too wide, the shim may 'roll' or shift under high clamping pressure, leading to instability. Conversely, if the notches are designed to interlock with the mold base, they provide superior lateral stability. Always assess the intended clamping force of your machinery and ensure the shim's cross-sectional area (the material remaining after the notches are cut) is sufficient to support that load without permanent deformation or 'creep.'