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Tips & Techniques

Smart Shim Measurements

Use shims as spacers to determine the amount to trim when installing cabinets and doors.

By Aron Jones Issue 323 - June 2024

When installing a prehung door over a finished floor, you need to find out exactly how far the surface of the floor is out of level in order to trim down one of the side jambs so that both jambs sit flush on the flooring. I have a quick and easy way to find that exact measurement. I use color-coded composite horseshoe shims of known thicknesses, typically 1⁄16 in., 1⁄8 in., and 1⁄4 in. Using a level the same size as the door opening, I slide the required number of shims under one end of the level until the vial reads perfectly level. The number and size of shims used will give you an accurate measurement of exactly how much to trim off one of the jambs. I use this trick when setting base cabinets and on other projects as well. There are several brands of shims available, but I prefer the horseshoe style, used by glaziers and tilesetters as spacers. They cost less than 10¢ each when you buy a pack of 200 or more.

—Aron Jones; Grand Manan, N.B., Canada

Edited and illustrated by Charles Miller.

From Fine Homebuilding #323

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