O ring: A flat ring made from synthetic rubber, used as an airtight seal or a seal against high pressures.
Oehman's survey instrument: A drill-hole surveying apparatus that makes a photographic record of the compass and clinometer readings.
Ohm's law: The law that the direct current flowing in an electric circuit is directly proportional to the voltage applied to the circuit, it is valid for metallic circuits and many circuits containing an electrolytic resistance.
ohmic: Pertaining to a substance or circuit component that obeys Ohm's law.
ohmmeter: An instrument for measuring electric resistance, scale may be graduated in ohms or megohms.
ohms per volt: Sensitivity rating for measuring instruments, obtained by dividing the resistance of the instrument in ohms at a particular range by the full-scale voltage value at that range.
OHV engine: NULL
oil burner: Liquid-fuel burner device using a mixture of air and vaporized or atomized oil for combustion.
oil cooler: A small radiator used to cool the oil that lubricates an automotive engine.
oil cup: A permanently mounted cup used to feed lubricant to a gear, usually with some means of regulating the flow.
oil dilution valve: A valve used to mix gasoline with engine oil to permit easier starting of the gasoline engine in cold weather.
oil filter: Cartridge-type filter used in automotive oil-lubrication systems to remove metal particles and products of heat decomposition from the circulating oil.
oil fogging: Spraying a fine oil mist into the gas stream of a distribution system to alleviate the drying effects of gas on certain kinds of distribution and utilization equipment.