Nut
Nut turns up in 2 fields: fasteners, maritime. Here is what it means to the people in each one.
Nut in fasteners
An internally threaded part that mates with a bolt or stud, graded so the bolt breaks before the nut strips.
A block of metal, usually hex, with an internal thread that mates with an external thread to complete a bolted joint. A correctly matched nut is designed so the bolt fails in tension before the nut threads strip, which is why nuts carry their own grades: property class 8 or 10 nuts for class 8.8 or 10.9 metric bolts, Grade 5 or Grade 8 nuts for inch hardware. Common styles include finished hex, heavy hex, flange, jam, castle and prevailing-torque nuts.
"Put a Grade 8 nut on that Grade 8 cap screw, a hardware-store nut will strip before the bolt ever gets to preload."
Nut in maritime
A nut is a projection on an anchor shank that secures the stock in its correct position.
A nut is a forged ridge or block protruding from the side of an anchor's shank, located just below the square hole where the stock passes through. It acts as a physical stop, preventing the stock from sliding down the shank when the anchor is deployed or retrieved. This ensures the anchor maintains its geometry to bite into the seabed properly.
"Inspect the shank near the nut for hairline cracks; that area takes a lot of stress when the stock catches the bottom."