A part number (often abbreviated PN, P/N, part no., or part #) is an identifier of a particular part design or material used in a particular industry. Its purpose is to simplify reference that item. A part number unambiguously identifies a part design within a single corporation, sometimes across several corporations. For example, when specifying a screw, it is easier to refer to "HSC0424PP" than saying "Hardware, screw, machine, 4-40, 3/4" long, pan head, Phillips". In this example, "HSC0424PP" is the part number. It may be prefixed in database fields as "PN HSC0424PP" or "P/N HSC0424PP". The "Part Number" term is often used loosely to refer to items or components (assemblies or parts), and is equivalent to "Item Number", and overlaps with other terms like SKU (Stock Keeping Unit).
The part design versus instantiations of it
As a part number is an identifier of a part design (independent of its instantiations), a serial number is a unique identifier of a particular instantiation of that part design. In other words, a part number identifies any particular (physical) part as being made to that one unique design; a serial number, when used, identifies a particular (physical) part (one physical instance), as differentiated from the next unit that was stamped, machined, or extruded right after it. This distinction is not always clear, as natural language blurs it by typically referring to both part designs, and particular instantiations of those designs, by the same word, "part(s)". Thus if you buy a muffler of P/N 12345 today, and another muffler of P/N 12345 next Tuesday, you have bought "two copies of the same part", or "two parts", depending on the sense implied.
User part numbers versus manufacturing part numbers (MPN) A business using a part will often use a different part number than the various manufacturers of that part do. This is especially common for catalog hardware, because the same or similar part design (say, a screw with a certain standard thread, of a certain length) might be made by many corporations (as opposed to unique part designs, made by only one or a few). For example, when referring to a "Hardware, screw, machine, 4-40, 3/4" long, Phillips":
Manufacturer A uses part number "4-40-3/4"-pan-phil", Manufacturer B uses part number "100-440-0.750-3434-A". Manufacturer C uses part number "TSR-1002". The business using such a screw may buy screws from any of those manufacturers, because each supplier manufactures the parts to the same specification. To identify such screws, the user doesn't want to use any of those manufacturer's part numbers, because
it would imply that one manufacturer is acceptable and the other ones aren't, and, it wishes to use a consistent format for the part numbers of all of the parts it uses. Therefore, the user devises its own part numbering system. In such a system, the user may use the part number "HSC0424PP" for that screw. There are also some national and industry-association initiatives which help producers and consumers codify the product based on a unified scheme to establish a common language between industrial and commercial sectors. For example:
The Iranian national classification and codification system known as Irancode is a 16 digit code to codify the products in a nationally unified manner. The U.S. government, and most especially its Department of Defense, has standardized various part numbering systems over the decades for it and its suppliers to use, such as the AN (Army-Navy) and MS (Military Standard) hardware classification and numbering systems. The Aerospace Industries Association maintains the NAS system (National Aerospace Standards), which is gradually replacing the AN and MS systems. The ASME provides a codification of fastener specifications in B18.24 Part Identifying Number (PIN) Code System Standard for B18 Fastener Products.
Significant versus non-significant part numbers In general, there are two types of part numbering systems: significant (a.k.a. "intelligent") and non-significant (a.k.a. "non-intelligent").
In a significant part numbering system, the part numbers are assigned intelligently, according to an encoding system, and thus they give an indication of salient characteristics of the component. For example, a screw may have the part number "HSC0424PP"; in this case, the letters indicate characteristics of the component: H = "Hardware" S = "Machine Screw" C0424 = "4-40, 3/4" long" PP = "Panhead Phillips" In a non-significant part numbering system, part numbers are assigned in some other fashion, such as sequentially or arbitrarily. For example, a screw may have the part number "1002", which may not tell the user anything about its thread size, shank length, or drive type. In a company, significant numbering systems help identify an item from its code rather than from a long description. However, variations can arise when codes are used by other companies, which may be your distributors, and can cause confusion. Non-significant part numbers are easier to assign and manage. They can still have some structure, such as a numeric category followed by a sequential number. Eg: 231-1002 (2=Hardware 3=Screw 1=Phillips, 1002 = sequential number). This enables more efficient data entry, using a keypad, which normally includes digits and dashes, and is operated one-handed, leaving the other hand free. Other benefits: people find numbers easier; in a warehouse, one can store products in numeric order (for example, in an aisle, numbers can increase from one end to the other).
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