What is this close-up picture? (WotsThat: Shackle metal texture (macro))

Question

What object is shown in this zoomed-in close-up photo?

FungalNet · Accepted Answer

Shackle metal texture (macro). A shackle's rated safe working load is deliberately set well below the force at which it would actually break, a safety margin engineers call a design factor, so it retains extra strength in case of shock loads or wear.

Answer: Shackle metal texture (macro)

More man made close-ups