The objective of this article is to guide
production and inventory management practitioners to a reasoned
and logical understanding of the issues surrounding part
numbering systems. The benefits and problems with significant and
partially significant part numbers, as well as use of alphanumeric
characters versus numbers only, short versus long part numbers,
and methods of assigning part numbers will be covered. A
recommendation for short, numeric-only, nonsignificant part
numbers assigned sequentially will be given and justified.
Finally, the interaction between part numbers and commodity coding
structures will be discussed with attention to today's relational
First, let's get some background (and a story)
out of the way. The APICS Dictionary (7th edition) defines
an item number as "a number that serves to uniquely
identify an item." This simple definition doesn't convey the
importance of the concept. Almost every business today runs on
information, and the part number is very often the piece of data
that ties all the other pieces together and makes them information
rather than just discrete, individual "datums."
Greene's Production and Inventory Control
Handbook* defines three kinds of part numbering systems
• Significant: "All
characters... represent a dimension, type of material, color, or
some other factor."
• Semisignificant: "Some of the
characters ... are significant; the balance are not and do not
represent a group or other factors."
• Nonsignificant: "None of the
numbers assigned has any significance."
Significant part numbers are also frequently
referred to as intelligent or descriptive part
numbers. The idea is relatively simple and seems logical and
harmless enough: Instead of relying on the description field in
our item master, why not encode a partial or full description of
the item's characteristics into the part number itself? Then,
anyone who knows the code will know all the important parameters
of the part, whether or not he or she has access to the MRP system
or a written document.
This argument is especially attractive to
people whose everyday work is somewhat detail-oriented, such as
engineers, computer programmers, finance professionals, anyone who
has to use MS-DOS, etc. I found the idea eminently sensible when,
as a young engineer, I was confronted with my first
"designer" part number, consisting of twelve digits that
indicated everything from the business unit using the part to the
part type to the size. The other engineers at my facility almost
took it as a matter of faith that the part number should be
intelligent, and thus we added more significance to the system,
bringing the number of digits used up to the maximum of fifteen
allowed by our system (which was viewed as a real limitation),
specifying the value of individual capacitors and resistors, the
technology of individual parts, and resulting in a series of
spectacular disagreements between perfectly well-meaning people
who felt their system was the best.
Our component engineering manager designed a
computer program to automatically assign the correct number for
a part, given all its critical parameters. All told, I am sure
that we spent a man-year on the system itself, using the talents
of our best and brightest to ensure that, among other things, we
never had enough letters in a row for the system to spell out any
Of course, once you have significant part
numbers, you must maintain them. Thus, we found ourselves changing
part numbers, or creating new bills of materials, when we shifted
production of an item from one plant to another, or when the
business group responsible for it changed, or when we found that
the initial description of a part was not quite correct and
therefore it required a different part number, even though the
part itself hadn't changed. And so we found out the first great
truth about intelligent part numbering systems: they require a
great deal of effort to create and to maintain.
Still, the benefits we perceived from the
system seemed to far outweigh the effort required to maintain it.
We thought our system was robust in an engineering sense because
it made it easy to detect errors. We were unaware of any of the
problems associated with intelligent part numbers other than the
effort required to maintain them. Only our poor materials
personnel and the general manager (who had a Ph.D. in physics
rather than an engineering degree) had a different perspective,
but somehow the engineers' ideas always seemed more cogent. That
is why it's important for us to understand the real issues and
arguments for and against intelligent part numbers.
We'll see that there are some valid
reasons for using an intelligent part numbering system. Benefits
can and do result from the use of significant part numbers.
However, many of the same benefits can be achieved by other means,
making significance unnecessary. More important, significant
part numbers bring some significant disadvantages with them,
including higher costs and cycle times, lower quality, increased
errors, and unnecessary work.
To be Continued
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