Engineers hammer is used to smack things and see what happens. You’re not meant to drive nails or shape metal with it, but it’s used to do inspections.

For example, a structural engineer inspecting a truss bridge might go and smack every stringer or strut near the river to the beam to see what happens. If the strut jiggles a bit, then the river has loosened and might need to be replaced.

If a bit of steel is heavily rusted, the engine might belt it really hard to see if it breaks due to deep corrosion, or if it’s just surface rust.

The sound you get from smacking a bit of steel can also tell you about the material, good steel will bong and reverb, bad steel will be dull and not reverb.