Definition
A temperature-measuring instrument with a long, slender, sealed metal probe (resembling a bayonet) that is inserted into the substance being measured. The probe contains a temperature-sensitive element, and the reading is displayed on an attached gauge.
Plain English
A thermometer with a long thin metal stem you push into something to read its temperature.
Context Anchor
Seen during aircraft servicing, preflight checks, and maintenance tasks that require a direct check of fuel or oil quantity.
Derivation
Named after the bayonet — the long blade attached to a rifle. The probe has a similar long, slender shape, which is where the gauge gets its name.
Why Pilots Care
Enables quick, tool-free gauge changes during maintenance without disturbing surrounding instruments.
Analogy
It works like a cap or fitting that lines up, pushes in, and locks with a short twist, while the marked part tells you the level of the liquid.
Intuition Check
Bayonet does not mean a knife here. It means the gauge uses a push-and-twist locking connection.
Example Sentence 1
The mechanic replaced the bayonet gauge after the oil temperature reading became erratic.
Example Sentence 2
During the preflight inspection the pilot noted the bayonet gauge reading normal oil pressure.