PLM Basics: Reference Designator and Find Numbers

PLM Basics: Reference Designator and Find Numbers

Some time ago, one of my readers wrote me a comment with the question about Reference Designators and Find Numbers. With all our interest to talk about modern technological trends, mobile, social software, understanding and clarification of basics is very important too. In the past, I wrote few posts tagged PLM Basics. If you haven’t seen it before, navigate your brower to the following link.

Online Reference Information
You are pretty much out of lack if you are trying to find this information online. Here is short info from Wikipedia.

A reference designator unambiguously identifies a component in an electrical schematic (circuit diagram) or on a printed circuitboard (PCB). The reference designator usually consists of one or two letters followed by a number, e.g. R13, C1002. Thenumber is sometimes followed by a letter, indicating that components are grouped or matched with each other, e.g. R17A, R17B.

Another source of information, which is probably less known – PLMPedia. This is an online project of created by LEDAS. Unfortunately, PLMPedia has no information about what is a reference designator.

Reference Designator (RD)
RD is normally a text field that belongs to Component in Bill of Material, that helps you to specify what this component does and how to find this component. In most cases, used when more than one component with the same Part Number need to appear in BOM. Reference designators can be used in various reports and Bill of Material views. The most of Reference Designator usages is to simplify your access to a specific Component / Part Number. The usage of Reference designators can be different between various systems in the industry. Normally, the information about Reference Designator usage belongs to BOM module.

Find Number (FN)
FN is a number that usualy set by Bill of Material management module when create line item in BOM. For most cases, I’ve seen, Find Number usually set automatically or manually as the incremental number for every row in Bill of Material. Find Number is a simple way to search, sort and organize lines in Bill of Material module.

I found usage of Reference Designator sometimes overlaps with usage of Find Number. I’m looking forward to hearing about your experience and common practices. I didn’t find much online information about terms and practices in product development and engineering. The usage of Reference Designators can be different in electronic industry compared to mechanical engineering.

Best, Oleg

*** photo in this blog post was imported from Flickr user Dano. The original file is located here.


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  • Oleg, this is a very interesting problem because many CAD applications don’t distinguish between the concepts. In particular, a BOM export from an ECAD system may have RefDes. An ECAD BOM may also export a line number as FIND, but the FIND isn’t consistent from one export to the next and therefore can’t be used as an anchor for determining differences from one revision to the next. This is regrettable, though completely understandable, since the design file doesn’t understand much about its own history.

    On the other hand, MCAD rarely seems to use RefDes as part instances, so the drawing will have multiple call-outs of a single FIND (such as four screws, each of which has a “bubble” using the same FIND). This approach at least provides an anchor for identify differences when transferring the data into the PLM/MRP.

    reference designator
    A reference designator is associated with a specific find-item on a structure, and is used to identify that item’s physical location in an assembly, or its logical location on a schematic. Each instance of the item has its own reference designator; there is usually a one-to-one relationship between a find-item’s quantity and the number of reference designators.

    find-item (or balloon or bubble or find) number
    A reference number that relates an item listed on a structure to its depiction on a related assembly drawing, without explicitly referring to the actual identifier (part number or document number). Find-item numbers for parts are typically integers greater than zero; documents listed on a structure may have find-items of zero, or may be assigned values in the same manner as parts.

    These are the definitions show at

    Kind regards.

  • beyondplm

    Ed, thank you for your comments and link share. I didn’t know about this site. I understand your point. RD is an “instance” of part for most of the cases. FD is a number related to a part rep in various locations- drawings, BOMs etc. This is my short def so far. Best, Oleg

  • Paritosh deshmukh

    Find Number Plays important role for BOMs released for manufacturing (ERP) through ECO Because, it help in Master production schedule and MS/MRP or ASCP plan this is because Find number are also used as processing sequence id of BOM assembly. As the processing sequence id are mapped to Job sequence id, which is internally mapped to lead time of the part in assembly. This way work order is created, which creates pick slips inventory to release the stock for manufacturing at right time.

    The whole process helps in smooth planning and defining production schedule.

    What concern is, the find number needs to be taken care when phantom parts are maintained in PLM and there BOM validation rule comes in picture.

  • There are subtle differences. In a BOM, every line item may be given a Find Number. This should be unique in the one-level BOM. The Find Number is sometimes used to point at specific parts in drawings etc. Mechanical Engineers use predominantly Find Numbers. If a BOM line has Qty greater than one, the Find Number may appear more than once in the drawing, as Ed A says in his comment.

    In electronics especially, each line item can have a Quantity higher than one (when the same standard component is used multiple times, e.g. in a Printed Circuit Board). Reference Designators are used to identify the individual items within that BOM line.

    For example, you may have in a PCB assembly a capacitor C12345 appearing with a quantity of 4 and a reference designator property like this “C1-C4”. This allows the board designer to identify each capacitor with C1, C2, C3, and C4, and still to have those 4 individual occurrences of the same item in one BOM line instead of 4 separate lines.

    This is useful in managing the component in the assembly: for example, when you want to replace a component in the BOM and you want to replace it in all positions it appears at once.

    Reference designators do not have to be unique across the whole BOM (even if that is someitmes useful), but they have to be unique in the BOM line only.
    For example, if you have 2 resistors in your PCB; R12345 appears with Qty=3 and R67890 appears with Qty=4, you may find that the BOM line for the first component has Ref Des = “R1-R3″, and the BOM line for the second component has RefDes =”R1-R4”; it is better, though, if you can make it unique on the whole BOM by picking for example “R1A-R1C” for the first BOM line, and R2A-R2D” for the second one. This will make the Ref Des equivalent to a Find Number. But in general, I think only the combination FindNumber-Reference Designator can ensure the compete identification of each indivisual occurrence of a component in a single-level BOM.

    How Reference Designators are asigned to individual component occurrences is normally determined by the ECAD package.How these are transported to the BOM depends on the ECAD package integration to the PLM system, and on how the PLM system can manage and store that information. .

    Teamcenter, for example, can pack or unpack BOM lines with Qty greater than one dynamically, interpreting the Ref Des string syntactically whenever possible.

    E.g. if someone enters a single BOM line with Qty=3 and RefDes=”R1-R3″, Teamcenter can dynamically unpack it in 3 BOM lines with the same component, same find number, Qty=1 and RefDes=R1, R2 and R3 respectively. The opposite operation of packing multiple BOM lines is also possible, if they have the same Find Number and Component.

    This is possible because Teamcenter’s data model and UI can effectively manage multiple occurrences of the same component in one or more BOM lines; this capability comes from its MCAD data management origins. Pure BOM based solutions are often not as good at that.

  • beyondplm

    Paritosh, thanks for this important clarification.Can you explain how it comes to the play with multiple levels and phantom parts? My initial assumption was that FN is unique in the specific “level”… correct? Thanks, Oleg

  • beyondplm

    Paolo, thank you for sharing this information. The difference between mechanical BOM and Electronic is important to understand. In addition, the issue of Find Number uniqueness. The occurrence model in BOM is the most appropriate method to handle this model. I’ve seen it in multiple PDM/PLM systems. Tnx, Oleg

  • Aravinth Rajendran

    Hi Paolo,

    Thanks for the description. I see your comment saying Find Number should be unique in the one-level BOM. So does this mean, Find Numbers present in multi level BOMs need not be unique. I mean a Find number used in the second level can be used in the third level also? If that is the case, when we see the entire assembly later, will it not cause any confusions for the design engineers as well as in the ERP systems? Please clarify.

    Regards, Aravinth

  • beyondplm

    Aravinth, I think FN is basically for one-level BOM only. The BOM actually can be for a whole product, but it will be presented as a flat list. Let’s wait for Paolo will tell us… Best, Oleg

  • Jim Hamstra

    Although the BOM mgt software (eg Teamcenter) may be content with duplicate Reference Designators across different part numbers, the ECAD software generally will not accept this nor work correctly. Generally ECAD software will insist that each Reference Designator must be unique at the PCBA level.

  • beyondplm

    Jim, thanks! A very important clarification. Especially for guys thinking about mechatronics… Best, Oleg

  • Prashant Dhonde

    Hi Oleg,

    Reference Designator is very specific to hitech industry whereas Find No you can find in Automotive industries
    Typically Reference Designators have series from R1 to R50 but is not the case with Find no, as you have mentioned Find No normally increases for every subsequent row
    Find no is also used in routing plan and I have also seen a case where specific find nos are given based on state of the raw material

  • beyondplm

    Prashant, thanks for this comment! You are narrow use cases, by saying RD is for electronic / high tech, and FN is for mechanical, mostly. For the simplicity, it makes sense. It is interesting how it may work for mechatronic examples? Have you had a chance to see them? Best, Oleg

  • Hcetin007

    i am trying to build up a fabric library. there are too many details like gramage, yarn densities, yarn number, yarn type:oe, carded, combed, fabric width, dyeing method, finishing and so on but may problem is that when a designer bring me a shopping garment to analyse than it is really difficult to find out all these details in a right way. what should i follow, detail or maybe a short description. but when you define the fabric in a short way than you cant understand if the new fabric is same as the one in system??

    thanks for kind advise

  • beyondplm

    Thanks for comment. I think, short name works. However, I’m not sure we are talking about the same problem. Can you, please, clarify with some examples? Best, Oleg

  • Eldad

    Interesting to read all the comments so far. The origin of FN as the term states, was realy to be able to ‘find’ the part on the drawing and relate it to the Parts List. Some of you remember the paper dwgs with the Title block and the parts list above it. You would identify a part in the list by its FN, and other attributes and will look for the FN on the dwg to see what it looks like. We even went further and assigned FN in a clockwise manner (on a complex assy dwg). Moving many years fwd, to PLM, the actual usage of the FN is more for historical purpose and is only to let the users see the parts in an organized manner. There are several PLM system that don’t even call it FN, and just assign a value in increments of 10 so users can identify the line item. As a metter of fact, the line numbers for a particular part will change depending how you view the BOM – IPL will repeat the FN per sub-assy, but if you view the BOM as a PL, the numbers will be sequential – so what is the real value?
    Mfg will assign a sequence number for their process which is unrelated to the FN (in most cases). In my openion, it’s another ‘left over’ from the paper period that most people don’t realy use, but – ‘we always have it’.
    RD – the commonality to FN is that the RD identifies the location of the component on th ePCB and allows for accounting of the components in the ECAD system. There are many cases that the PCB is only partially populated and so not all the components are being used. The RD method allows the systems to easily identify the different configurations based on population of the components. If you crate a BOM for the PCB, every components will have a FN and a RD.
    Where FN do not play a role in the business processes, the RD do!
    My 2 cents…

  • beyondplm

    Eldad, thank you for your comment and insight! I agree, FN has a lot with a history of paper drawing and assembly that connected part list to the drawing. RD is providing an additional (structured) “part information”, which embedded into part list/bom (especially important for electronic designs). Best, Oleg

  • Paritosh_deshmukh

    In PLM, SuperStructure BOM, which is at the level of Product line, has Phantom BOM, which acts like a bucket or library item ( child parts). This way Manufacturing Base assemblies are tied to each bucket.

    But when the same BOM goes in Planning system, the superstructure is transformed as sales BOM. which has multiple SKU and Finished Good Assembly.

    The forecasting planning percolates the Demand from Product line to product family, Models, Options, SKUs and than to Assembly finally leading to item level AND this demand is bumped agains supply, which results in planned orders.

    The planned orders results in production workorders or purchase orders, based on excess supply and demand and Make or Buy attribute.

    When it comes to workorder, the manufacturing of BOM is completed, its is backflushed, which results in many things like inventory update and Completion of SKU, when it comes to BOXing and Carting of multiple items Selected Options are completed, This way whole Model is packaged in warehouse and shipped to customer.

    The whole process is tracked through the sequence id, which is nothing but Find numbers in PLM BOM.

  • beyondplm

    Paritosh, thank you for sharing this excellent example! What is very interesting is how Find Number used for traceability of Parts in PLM BOM. What is the format of find numbers you are using for these cases? Is it a simple string? Part Number combination? Id? Thanks, Oleg

  • Deshmukh2

    Hi, Find Numbers format used is just number. But tracing and logic is based on combination partnumber,part description and find number (commodity code, region goes as encoded) the part description has all the commoditiy code information in ERP system. this mapping is master cross reference file for all the supply chain validations, integrations in ERP. it gets updated based on commodities.

  • beyondplm

    Deshmukh, thanks! I see it a very good example and use case. So, yet another usage of Find Number, in my view. Can you, please explain a reference to “commodities”? I didn’t get it… Oleg

  • Paritosh Deshmukh

    Commodities are combination of distinct part classes and part types. every part class represent commodity, like capacitor, resistor where as part type is like resistor of various subdivision.
    We call be various names like commodities and commodity codes or Item category and item category codes.
    the business process defines Commodities and codes on the lines of UNSPC standary. this standard runs throughout the organization division and departments. therefore based on region, labeling, packaging, engineering, mechanical, the commoditiy codes are mapped. so starting with part creation/material registration the commodities and codes are created in PLM and suffix of part class and parttype goes in description.
    Downstream application recognises the information and mapped to respective department commodity. this is how, dispersion of part information is percolated to manufacturing application.

  • beyondplm

    Deshmukh, thanks! I’ve got you now… Best, Oleg

  • JP

    Thanks Paritosh for the explanation. One question through. Why can’t the system use Part number for all these activities downstream instead of Find Number?

  • Shashikant

    Thanks for the Post.

    Still I am not sure why to use Find number in multiply of 10 in TCe. Is it somthing related to space consumed on server by the BOM line in assembly?

    Answer will be appreciated a lot..


  • beyondplm

    I guess, this is part of old technique how to keep space for sorting of BOM based on FN. You have 10, 20, 30…. and then you can add 15, 16 and it will be still ordered in the right way.