Naphtha: generic term describing a variety of light petroleum distillates such as mineral spirits and many petroleum solvents.

Naphthenes/naphthenic base or oil: also known as cyclo-paraffins: a class of saturated hydrocarbons with a ring structure, distinct from both aromatics and paraffinic hydrocarbons; because of their low wax content, naphthenic base petroleum oils have low pour points and good solvent properties (see hydrocarbon).

Naphthenic acids: complex organic acids obtained from the gas oil cut of crudes, used in the manufacture of soaps, paint dryers and emulsifying/demulsifiying agents.

Neatsfoot oil: pale yellow animal oil made from the feet and shin bones of cattle, principally used as a leather dressing.

Needle bearings: rolling bearings with rod-shaped cylindrical rollers that are long and thin in relation to their diameter.

Neoprene: chloroprene polymer synthetic rubber with high resistance to weather, chemicals, petroleum oil and heat.

Neutralization (“neut”) number: serves as an indication of the acidity or alkalinity of an oil. For acidity, the number is the quantity of base expressed in milligrams of potassium hydroxide (KOH) required to neutralize one gram of oil to a specified end point. For alkalinity, the number is the amount of acid expressed in milligrams of potassium hydroxide required to neutralize one gram of oil. See strong acid, strong base, total acid number (TAN) and strong base number (TBN).

Neutral oils: unfiltered lubricating oils of low or medium viscosity obtained in petroleum distillation and prepared without chemical treatment; they are so named because they have not been treated with an acid or an alkali.

Newtonian fluid: fluid classification by response to shear rate and shear stress. The ratio of shear stress to shear rate is a measure of a fluid’s viscosity; when that ratio remains constant at any shear stress or rate of shear, the fluid is termed “Newtonian”.

N-heptane/normal heptane: hydrocarbon compound (C7H16) with an octane rating defined as zero; used as a reference fuel ingredient in motor fuel octane number tests.

NLGI: National Lubricating Grease Institute; an organization of grease manufacturers that works with ASTM to develop technical standards.

NLGI number/NLGI grade: arbitrary numbers assigned by the NLGI that classify greases by their hardness, as determined by the cone penetration procedure (ASTM D-217); numbers range from 000 for the softest grease to No. 6, the very hardest (see consistency, penetration).

NLGI automotive grease classifications: specialty or mult-purpose greases meeting the requirements of ASTM D-4950 for chassis (category LA or LB) or wheelbearing (category GA, GB or GC) can be registered with NLGI and subsequently marked with a trademarked NLGI symbol that shows which performance categories the grease meets.

Normal plane (gears): in helical gears, the plane perpendicular to the teeth.

Nuclear Magnetic Resonance/Magnetic Imaging: Nuclear Magnetic Resonance (NMR) provides non-destructive, magnetic radio-wave analysis of new and used lubricants, especially to pinpoint chemical changes in carbon, hydrogen an phosphorus in lubricants; may also be useful as a tool for condition monitoring of gear oil and motor oils.

Non-Newtonian fluid: fluid requiring an initial stress to start flow, as the ratio of shear stress to shear rate does not remain constant. In this category, greases are among the substances that do not exhibit viscosity as Newton defined it; “apparent viscosity”, depending on the rate of shear, can be computed for such materials, but the viscosity derived will apply only to the shear rate used in making the computation.

Nonsoap grease: grease thickened with something other than a metallic soap, e.g., clay, carbon black, silica gel or one of many synthetic organic compounds.

Norma-Hoffman bomb test: (ASTM D-942) a static accelerated grease oxidation test that measures the rate at which a grease absorbs oxygen.

Normal/standard pressure: unless otherwise specified, this term refers to 14.7 psi or 760 mm of mercury, i.e., normal atmospheric pressure at sea level.

Normal/standard temperature: in most laboratory work, 25°C, equivalent to 77°F.