Answer: I’m asked this question all the time, so I’m surprised that we never touched on this before. In short, OEM means Original Equipment Manufacturer and NOS means New Old Stock…a confusing term if there ever was one. Other related terms that you might encounter in your search for parts are NORS (New Old Replacement Stock) and Reproduction Part.
An NOS part is one that was produced long ago specifically for use by the manufacturer of an automobile to be used in the production of that automobile, or possibly for inventory in the parts department of a new car dealership, or a distribution center. It may have been produced by the automotive manufacturer, or by an outside supplier. It would not have been found in an automotive parts store. Sometimes found in its original packaging, which will always have the part number, it is considered the “holy grail” of replacement parts. Condition of NOS parts vary greatly as by definition (at least as it applies to classic cars) they have been sitting in warehouses, or on parts shelves, or in garages, or cornfields for many decades. Depending on the rarity of the part, its condition, and its application, the prices of some NOS parts can be staggering. For example: An NOS set of front shock absorbers for a 1964 GTO, in the original box, recently sold on eBay for $990.00. I’ve seen NOS fenders sell for thousands of dollars and other rare NOS parts can sell for much more.
OEM parts would have been produced by an outside supplier, but it would have to be the same supplier that originally supplied the part to the manufacturer. These parts would typically have been shipped to dealers to replenish inventory, as well as to automotive parts stores. OEM parts are functionally the same as NOS parts, but there is no guarantee that they are cosmetically identical. In fact, many are not, and can vary significantly in appearance from the original part. An OEM set (in this case manufactured by Delco) of front shock absorbers for the same 1964 GTO would sell for a fraction of the cost of the NOS set. Perhaps $150.00.
NORS parts are simply aftermarket replacement parts. They would have been found in automotive stores, but they would never have been found in a dealer inventory or parts department. In most cases the packaging and the part would be badged with the name of the parts manufacturer, such as Fram, TRW, Moog, or NAPA. An NORS set of
front shock absorbers for a 1964 GTO would probably cost in the range of $50.00, possibly even less.
Reproduction parts are reproductions of original, presumably NOS parts. These parts are generally reproduced in response to a large demand from the collector car market. Reproduction parts are very popular and very common on collector cars, and they are far less expensive than comparable NOS parts. They are also subject to wide variations in quality. For example, some reproduction body parts are often dimensionally different from the original parts that they are intended to replace. Some of the major manufacturers such as General Motors and Ford have licensed the rights to reproduce original General Motors parts for the collector car hobby. These parts are generally high quality and are often indistinguishable from the original parts that they are intended to replace. A reproduction set of front shock absorbers for a 1964 GTO is advertised on a major website for $74.00.
When the need arises to replace a part on a collector car, the source of that part can potentially become important. How important it becomes is determined by the originality of the collector car, as well as your desire to maintain that level of originality, as originality translates into value.