Steel Manufacturing Blog: Keeping it Steel

Plastic Shims: Evaluating Cost, Strength, and Durability

Posted on Wed, May 22, 2024 @ 11:26 AM

Often when projects require shims the default material is automatically steel. This is often overkill in terms of performance and required compression strength. As a possible option, Construction Grade Plastic Shims offer exceptional strength and durability.

Fig. 1 Various Plastic Shim Sizes

Plastic Shim AssortmentThe main advantage plastic shims (Fig. 1) offer is lower cost. Not only is the raw material less expensive, but the processes of manufacturing and transporting plastic shims adds to the savings. A slotted steel shim starts as a master coil of steel and passes through many steps in the manufacturing process. As well, there is always drop created in shim production and if the location will allow exposure to moisture a steel shim needs to be galvanized. This again adds expense and time.


Fig. 2 Shows 3” x 4” 
Plastic Shim Pack 
Arranged by Thickness



Stock size plastic shims (Fig. 1 and 2) are injection molded. The entire process starts and ends in one injection molding machine and a cycle, taking as little as 3 minutes, can produce 30 to 50 shims depending on their size. They will not rust and can be easily transported.


Fig. 3 Korolath Plastic Shim
Machined to a Wedge

Korolath-Slotted-Wedge-ShimFig. 3 Shows a Korolath plastic shim cut to to 3” x 4” with a slot, but then machined to a wedge 3/8” down to 1/16”. If a plastic shim has to be made to order as is frequently the case with our Korolath shims, the material is much easier cut and machined, which helps keep costs under control.

At issue when determining shim material is compressive strength. Most construction shims exist as spacers sitting between two surfaces and will typically have even, consistent pressure throughout their service, so impact is not an issue. The compression test results shown on our website illustrate the strength plastic shims can provide.

Note: When testing plastic shims, they are not compressed until they break. They are taken to the point where permanent deflection occurs. Like all materials, plastic compresses or “deflects” under pressure. When the pressure is removed, it will return to its original size. Permanent deflection is when the pressure is removed and the shim does not return to original size.

As an example, look on the Compression Test Chart for item # 402-6 x 1/8. In two separate tests it withstood 75,000 lbs. This shim is 3” x 4” with a slot so the actual surface area is approximately 9.6 sq. in. Rated at 75,000 lbs, this plastic shim provides 7,812 psi. of compressive strength.

                                                                                                                                 Fig. 4 Injection                                                                                                                                           Molded Wedge
                                                                                                                     Plastic Shim #402-6W x 1/4

The Steel Supply Company specializes in Shims including:402-6W x 1-4

  • Slotted Steel (105 stock sizes)
  • Hot Dip Galvanized Slotted Steel ((62 stock sizes)
  • Slotted Plastic (60 stock sizes)
  • Solid Plastic (75 stock sizes)
  • Korolath (unlimited configurations)

Also, regardless of Steel or Plastic, any shim can be made to your exact requirements.

Call or email for a quote today


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