In addition to a picture of the part, he also takes a picture of a vernier caliper gripping the part. Now your scale is built into the picture, and you can edit out the caliper later.

Along its shiny sides you'll find a four-inch Vernier caliper (with scales of 0.1mm and 1/16-inch), a metric screw-thread scale and a tire-tread depth-gauge.

I can use the vernier caliper for this again, as it has both metric and imperial measurements on it. I need to measure the diameter here, the distance across the entire bolt head. That's 13 ...

This 6-inch caliper can swap freely between imperial and metric units and can even record units in fractions. It has an auto-off feature to preserve battery life. Sold by Home Depot ...