Calibrate the micrometer you will use to measure the bearing. Open the micrometer and fit the gauge block between the measuring tips. Turn the thimble to close the micrometer until the measuring tips contact the block. Read the measurement to ensure a margin of error that is no more than plus or minus 0.0005.
Write the following in a column on a piece of paper: d =, D=, B/T=. Make a notation at the bottom of the paper that d=inside diameter, D = outside diameter and B/T = width diameter.
Measure the inside diameter first. Open the micrometer to the approximate size of the inside opening. Slowly adjust the micrometer until the measuring surface on each side of the micrometer makes contact with each side of the inside opening. Write down the measurement on your paper.
Clear away buildup of grime and debris on the outside of the bearing to ensure a more accurate measurement. Measure the outside diameter of the bearing using the same technique in step 2. Write this measurement on your paper using a capital letter "D" for reference.
Measure the width of the bearing using the same technique described in step 2. Write down the width measurement noted as "B/T".
Use the measurements to find the part number at a bearing dealer, or enter the measurements at a bearing dealer website to search for your part number.