@MartyE posted:
What a GREAT photograph! Note the special Machinist's Hammer the Inspector is holding in his right had. The various machined diameters on the head, plus the length of the head, are used for making all sorts of "known dimension checks". Also, the inspector uses the hammer to tap on bolts & rivets in order to determine whether they are properly tightened.
Those special Machinist's Inspection hammers are still used today when inspecting diesel units, and I still have mine hanging on a hook in the garage.