Continue to Site

Welcome to MCAD Central

Join our MCAD Central community forums, the largest resource for MCAD (Mechanical Computer-Aided Design) professionals, including files, forums, jobs, articles, calendar, and more.

O-Ring size differences in an Assembly


New member
I would like to have an O-Ring with the same PN# XYZ to have two different Inside Diameters in a Assembly. Does anyone know how to write a relation that will control the I.D.'s of the O-Ring in the assembly? One of the O-Ring's is in a sub-assembly of the Top Level while the other O-Ring is directly in the Top Level assembly.


New member
An o-ring can have as many different sizes for as many different locations it's used in.

My recommendation is to family table it, use the installed dimensions and create an instance for each location it's used in, eg:

12345678 Generic

12345678_891011-1 One instance used in 891011 assembly

Always good to include a counter (-1) as you may have multiple instances in a single assembly..


New member
The BOM can become a problem with instances from family tables. If you're on Wildfire the flexible component functionality finally gets you what you really need to handle these types of situations.


New member

We use Intralink and have a user-defined attribute called Title.

We just add this to the family table and can then give each

instance it's own, unique name to appear on the BOM in our

assembly formats.

I would assume the same would work for a system-defined

attribute but have never tried it.


The way you describe, you can not get the quantity to show up on BOM using report quantiy or can you?



New member

The way we change the name of a component and/or an assembly is to add a repeat region relation to the BOM. If you can access PTC's knowledge base, see this link - or send an e-mail and I will give you more detailed instructions.

Best Regards



New member

The attached ZIP file contains a JPEG image of a BOM on

on of our Pro drawing formats. The last item in the BOM

is an instance of a generic used four times in an assembly.

The title parameter allows different lenghts to show on the

BOM and the BOM created with Pro/REPORT in our formats

captures the quantity.

Hope this clarifies.



New member
The focus is not to change the component or the part number that shows up in a repeat region BOM, not the part name. This situation is characteristic of other parts that may also change shape as a result of assembly or manufacturing process, i.e. rivets, bends, springs, but in this case it's o-rings. The technique I use was created by another manufacturer in our area. I learned it from them at a user group meeting.

It's called Physical & Phantom modeling. First the Physical Model (PN#x010_xxx) the O-Ring that will control the drawing. This mdoel has all the required dimensions and tolerances per the application and in it's purchased state. This model also has a family table. The table has the original part number (X010_xxx) with underscore_extensions for example

x010_176, x010_190, x010_202 which the extensions represent the changes in the I.D. of the O-Ring. These models get assembled into the assembly. Then the Phantom Models. The phantom models are created for one purpose and

one purpose only. To have the correct PN# to which the parts are order through our purchasing department show up on the BOM. This model named phantom_X010 has a family table with only one member. The member name is X010...the correct PN# of the o-ring. The model consists of a revolved

surface the same x-sec and i.d as the assembled o-ring and is assembled in the exact location as the physical o-ring. Then you just remove item ex.(x010_176) from your repeat region and your left with the x010 part in the BOM.

P.S. I still need a solution to have the I.D. of the same o-ring part number be different when assembled to one sub-assembly and have the I.D. of the o-ring different in the top assembly.


Articles From 3DCAD World