The Steel Supply Company provides shims to a variety of construction trades. Solid or Slotted, Plastic or Steel. It should be noted that by solid we mean non-slotted, or what is sometimes called "Plate Shim." The plastic version of these plate shims is still solid throughout. This is differentiated from some plastic shims on the market that are actually hollow in the core. Shims that are not solid cannot deliver the compressive strength required for most construction projects. The plastic shims shown in Fig. 1 are all solid throughout. Note the slotted plastic shim on the left of the image. It's actual dimensions are 4" x 6" x 1/2" thick, solid throughout, and is compression rated to support 90,000 lbs. before permanent deflection occurs. Based on its surface area, that is approximately 4,500 psi.