What Is a Shim?

Shims. Copyright/Courtesy Lee Wallender; Licensed to About.com

Within the world of home renovation and building, a shim is a thin wedge of wood generally used for positioning window or door units within their respective openings.

A common size for wood shims is 9" long and 1 1/2" wide. The thicker end may be around 3/8", tapering down to 1/16" or less.

Shims can be made either of wood or composite plastic. The composite plastic shims have scores that allow you to snap off the shim at the correct length rather than cutting them off with a saw.

After the door or window unit is placed into the opening, the shim is gently tapped into place by a hammer.

While it is possible to cut your own shims with a tablesaw (and this may be done in a pinch), I recommend making the small investment in "store-bought" shims. These shims are of uniform shapes that are difficult to achieve by yourself with a tablesaw.

Also Known As 

  • wood shim
  • cedar shim