Mechanical link

ISA 5.1-2009/2022 (instrument line symbols)

Drawn as

A thin line with a small open circle at each end (pivots).

Meaning

Mechanical connection between devices: a float to a valve, interlocked PSV changeover valves, or a key interlock. Not modelled; note the interlock.

Variants

Legends differ: some draw a plain line with "MECH. LINK", others a dashed line with circles
Key interlocks are often shown as a dashed line with a key symbol or "KI"

Not physical hardware. Read it, then skip it in the 3D model.