Part Numbering

Any part database necessarily requires some index by which a part number can be referred uniquely. To a human, this is usually a two-part index composed of the manufacturer and the manufacturer's part number. Together, they usually refer to a unique part. It is often helpful to consolidate those two indices into a single reference. This we'll call an internal part number. (It is also often called a SKU or Stock Keeping Unit.) This allows people within an organization to communicate more effectively with a single index into a shared database.

Aligni supports several ways to establish internal part numbering. Admittedly, the choice often leads to a contentious debate. Here, we list some of the choices and illustrate the advantages and disadvantages. The part numbering styles we discuss fall under four general categories:

  • Derivation of Manufacturer’s Part Number
  • Formatted Part Numbers
  • Prefix or Subgrouped Part Numbers
  • Straight Numbering

In all cases, it is generally assumed that the internal part numbering must be unique so as to avoid contention between two different parts. Sometimes, an organization may decide that original manufacturer’s part numbers are unique enough that no internal numbering is required. This is really just a special case of the first category.

Straight Numbering (RECOMMENDED)

Examples: 100982, 9001234, 83001193

Straight numbering is really just assigning sequential numbers (to guarantee uniqueness) to parts as they get added to the database. The only challenge is to decide up-front on how many digits to use. Even with nearly a million parts to contend with, one can see the benefits in compression here — only six digits are required to uniquely identify any part in the database.

The chief disadvantage is that the number means nothing. It is only an index into a database and therefore requires access to the database to derive meaning.

There are several advantages, though. First, it is less subject to human error since it is shorter and can easily be held in short-term memory. Second, it is concise. Third, since it has no special characters, software support should be a foregone conclusion.

Aligni is a product which accentuates the benefits of this style. Since the software is available online, it is ubiquitous and readily available, so reference is easy and quick. Searches and “auto-complete fields” within Aligni are designed to use the more meaningful manufacturer’s part number and display the shorter straight number right next to them, so you reap the benefits of both.

You might want to consider starting your part numbers at a higher number so that the number starts with a “1”. Some spreadsheet applications might remove leading zeros making “000982” appear as “982”. This won’t happen if you start at “100000”.

Derivation of Manufacturer’s Part Number

Examples: SN74LS04DRE4-ND, 74LS04DRE4, 595-SN74LS04DRE4

This style attempts to resemble the original manufacturer’s part number as closely as possible. Sometimes, certain characters may be substituted in order to maintain a consistent character set. For example special characters such as + or * may be replaced with underscores or eliminated entirely. Additionally, as is the case with the (-ND) in DigiKey part numbers, a suffix may be added to indicate that this is an internal part number.

The biggest advantage to this style is familiarity. The original manufacturer’s part number is likely familiar to the engineer and so would the derived part number.

Unfortunately, there are several disadvantages to this style. First is that collisions may occur where similar parts are offered by multiple manufacturers. (the catalog vendor Mouser uses a numeric prefix before the part number to differentiate manufacturers.) For ordering purposes, it is usually preferred to offer a globally-unique part, including resolution of the manufacturer. Also, if a manufacturer decides not to make a change to a part number during a change to that part (for example, during the change-over to RoHS-compliant parts), your database is also necessarily bound.

Finally, though perhaps most significantly, manufacturers establish rules for part numbers so that they can “future-protect” the uniqueness of these parts. This includes using many characters and fields so that variations are specified. This is most often seen with discrete passive electronics where parameters such as value, tolerance, material, or temperature range are components to the part number. While this may be handy to establish a large product line of hundreds of thousands of parts, most organizations don’t need to refer to this full space and can do so in a much more compressed manner. These cryptic numbers are often the cause of many human translation errors, as well.

Formatted Part Numbers

Examples: R-0603-47K0-10, TI-74LS04-SO8

Formatted part numbers are basically what manufacturer’s use to build out their external (customer-facing) part numbers. Certain fields are established as meaningful and an attempt is made to keep them consistent across the database. Important parameters become part of the part number itself to facilitate easy identification.

The disadvantages of this method are typically realized only minutes after attempting such an endeavor. Enough information must be included in the format to avoid collisions. But too much information means that part numbers become excessively long. Software may need to be enhanced to enforce the complicated rules or errors are likely. At some point, the part number itself becomes the part description and is redundant. As with a manufacturer’s part number, this method is also subject to human error in translating a long and cryptic string. Finally, as a database grows, this method is increasingly difficult to maintain. In particular, new types, values, tolerances, materials, packages, etc. will invariably be introduced that weren’t part of the original specification.

Prefix or Grouped Part Numbers

Examples: 595-SN74LS04DRE4, 001-060304K7, 023-000123

This is really a slight generalization of the other three methods discussed here. A short prefix is used to identify the manufacturer or part type (such as capacitor, switch, resistor). Since the manufacturer’s part number is usually unique within that manufacturer’s product line, uniqueness is guaranteed. (Although this is not always the case. Some organizations may require a greater granularity than the manufacturer maintained with their part numbers. This was recently the case when some manufacturers chose not to differentiate their RoHS from non-RoHS parts during the transition.)

Generally, the same advantages and disadvantages apply here, depending on how the remainder of the part number is constructed. The question is really what value the additional prefix or grouping provides. In the case of derived part numbers, it’s a welcome addition. In the case of straight numbers, however, the prefix offers little.