How to use an inside spring-joint caliper
Step 1 - Close legs of caliper
Close the legs of the caliper by turning the adjusting nut so that they can be inserted into the space you are measuring.
Step 2 - Position caliper inside object
Position the legs of the caliper inside the object you are measuring.
Widen the legs with the nut until the measuring faces are gently resting against the circumference of the diameter of the hole or bore.
Step 3 - Tighten adjusting nut
Tighten the adjusting nut so that there is only a slight resistance when the caliper is removed from or reinserted into the inside diameter.
Step 4 - Remove calipers
Remove the calipers from inside the internal diameter. Now you have set the caliper, it is time to take the measurement.
Step 5 - Transfer measurement
To find out the width of the inside diameter, use an instrument with a scale like a ruler or micrometer.
Measure across the measuring faces to get your reading.