Measure_bearing To measure the bore of a bearing you can use a vernier caliper like the one shown.
Insert the outer anvils of the caliper into the bore as shown and open the caliper until the bearing and caliper are a good fit about each other. Now read the value on the caliper.
In the absence of a caliper a good quality steel ruler will suffice.
measure bearing To measure the outside diameter of a bearing place the jaws of the caliper around the bearing and close it until its a good fit but not tight, now read the value from the caliper.
measure bearing In the same manner as you measured the outside diameter measure the width as shown.