--- title: Defining Essential Geometrical Dimensions for Part Sizes description: "# Motivations This is written for BIM modelers who want to create new Part Size of the Gravity and Pressure Network Part Catalogs. Part Catalogs, especially Pressure Network Part Catalogs, contain properties that are poorly defined, but nonetheless are essential…" url: "https://civilwhiz.com/docs/defining-essential-geometrical-dimensions-for-part-sizes/" updated: "2026-08-17" category: Networks --- # Defining Essential Geometrical Dimensions for Part Sizes # Motivations This is written for BIM modelers who want to create new Part Size of the Gravity and Pressure Network Part Catalogs. Part Catalogs, especially Pressure Network Part Catalogs, contain properties that are poorly defined, but nonetheless are essential for the inner workings of Civil 3D. This is a post about how to get the “general outline” of the Pipe/Structure, which is important for clash analysis purpose, or to compare the dimensions from other software during synchronization process. It doesn’t concern itself with the nuts and bolts of the fine detail rendering, in other words, it concerns only with the “essential dimensions” of a gravity or pressure Part Size. # Gravity Part Catalog ## Add new Part Size You can create new Gravity Part Size by using the **Part Builder**, and you can access it via **Design->Parts Builder**, as shown below ![Parts Builder](https://civilwhiz.com/wp-content/uploads/2025/07/Parts-builder.png) Then, you will be asked to select/create a **Part Family**, such as **Concrete Pipe SI**, in order to add a new size. To add a new size, you can just right click on the **Size Parameters**, **Edit Configuration/Calculations/Values** to add in new part sizes. ![Edit Configs](https://civilwhiz.com/wp-content/uploads/2025/07/Edit-configurations.png) ## Pipe Roughly speaking, **gravity pipe** can be divided into 2 shape categories, the **rectangle** and the **circular**. The critical dimensions that govern **circular** pipes are **Pipe Inner Diameter (PID)** and **Wall Thickness (WTh)**. You can define them in **Parameter Configurations** by clicking on the white paper icon, as shown below ![Parameter config](https://civilwhiz.com/wp-content/uploads/2025/07/Parametr-configuraitons.png) ### Nominal diameter is not necessarily PID Do not automatically copy a pipe’s **Nominal Diameter (DN)** into **Pipe Inner Diameter (PID)**. DN identifies a standardized size; PID controls the bore drawn by a circular gravity-pipe recipe. They can have the same number, but they are not the same property. For example, the [Malaysian VCP sizes](/docs/circular-gravity-pipe-sizes-in-malaysia-ms-standards/) include the following model inputs: | Nominal size | Modelled PID | Modelled WTh | Modelled barrel OD | | --- | --- | --- | --- | | DN 150 | 150 mm | 17 mm | 184 mm | | DN 600 | 597 mm | 64 mm | 725 mm | For this simple circular model, `barrel OD = PID + 2 × WTh`. The modelled barrel OD does not include a wider socket, coupling, or joint. Use the manufacturer’s detailed product drawing when those dimensions affect fabrication or clash clearance. The critical dimensions that govern **rectangle** pipes are **Pipe Inner Height (PIH)**, **Pipe Inner Width (PIW)** and **Wall Thickness (WTh)** correspondingly. **Take note for pipe, the outer dimension like Outer Diameter or Outer Width/Outer Length doesn’t by itself exist. So they can’t count as the dimensions provided by Part Catalogs** ### **Circular** or **rectangle** pipe? Inside the [\*.xml there](/docs/hacking-the-gravity-network-catalog/#4-toc-title) is a **CSS** name section (**SweptShape** context section). There are 4 choices: - **SweptShape_Circular**: **PID** will be read - **SweptShape_Rectangular**: **PIH/PIW** will be read - **SweptShape_Elliptical**: **PIH/PIW** will be read - **SweptShape_EggShaped**: **PIH/PIW** will be read So in this sense, all shapes saved for Circular shape are rectangle Pipes. ## Structure Again, Structure can be roughly divided into two broad categories, the **Cylinder** and **Cuboid**. The critical dimensions for Cylinder structure are **Structure Diameter (SBSD)** and **Structure Height (SBSH)**. The critical dimensions for Cuboid structure are **Structure Height (SBSH)**, **Structure Length (SBSL)**, **Structure Width (SBSW)**. Again, you can only define for the **Diameter** dimension or the **Width/Length** dimension, but not both. Take note that in both cases, - you can also define **Wall Thickness (WTh)**, but that is not mandatory. It could be useful for rendering the structure, but it’s not that important to get the “actual sizes” of the structure - For structure, Inner dimensions such as **Inner Diameter** aren’t strictly required, but I also see it define in some of the default Part Families shipped by Autodesk. ### **Cylindrical** or **box** structure? Inside the [\*.xml there](/docs/hacking-the-gravity-network-catalog/#4-toc-title) there is a **SBS** name section ( **StructBoundingShape** context section), which informs about what type of the pipe/structure it is: - **BoundingShape_Cylinder**: **Structure Diameter (SBSD)** will be read - **BoundingShape_Box**: **Structure Length (SBSL)** and **Structure Width (SBSW)** will be read. ## Modelling consideration Civil 3D ships with quite a number of pipe/structure stock templates, that you can use by just adding the size of your own choice to the same topology model. This is the easiest way to get started on creating your own part catalogs. If you are ambitious you can try to create your own topology model, by using [Part Builder to create your own 2D or 3D model of the parts](https://help.autodesk.com/view/CIV3D/2026/ENU/?guid=GUID-55FDE358-B470-4E95-97E8-016F1CF63528). # Pressure Part Catalog ## Add a new Part Size To add a new pressure pipe/fitting or appurtenance, you will need to use a separate program coming together with Civil 3D installation, the **Content Catalog Editor (CCE)**. ## Pipe There are a few parameters concerning pressure pipes that deserve some examinations ![pipe parameters](https://civilwhiz.com/wp-content/uploads/2025/07/diameters.png) - **Diameter Outside (mm)**– the outside diameter. This is what Civil 3D will use to generate the outer profile of the pressure pipe - **Diameter Inside (mm)** – the inner diameter - **Thickness (mm)** – the pipe thickness. From what I understand, it doesn’t play directly into the rendering. - **Nominal Diameter (mm)** – the nominal diameter of the opening, which the pipe has 2, and hence, two rows of nominal diameter as shown. Since the nominal diameter is on per opening basis, my guess is that they are useful only as design check and don’t feature in geometry generation. But I’m not really sure on this point - **Outer Diameter (mm)** per opening – Astonishingly, each opening will have its own **Outer Diameter**! How is this diameter different from **Diameter Outside**, I don’t know. I can only guess that for pressure pipe, **Diameter Outside** ( on pipe basis) is being used, but **Outer Diameter** (on opening basis) is not. **Bottom line:** to correctly model a pressure pipe in geometry, you will need to define **Diameter Outside**, **Diameter Inside** *and* “Thickness” correctly and consistently. ## Fitting/Appurtenance Pressure pipe has 2 fix openings, but depending on the type of fitting or appurtenance, the number of opening can vary from 1 to 4. Given that **Nominal Diameter** and **Outer Diameter** are permanent fixtures of opening, I would have guessed that **Outer Diameter** and **Wall Thickness** would be used in rendering the geometry of Fitting/Appurtenance’s opening. Also note that **Nominal Diameter**, **Outer Diameter** and **Wall Thickness** all seem to be independent of each other; there is no formula that link between them. Therefore, as a BIM modeler, you should ensure that all the numerical values are consistent and make sense physically. ## Modelling consideration Modelling fitting and appurtenance are different than modelling pressure pipe. Whereas modelling pressure pipe is easy– you can just **Import Part** without a `.content` file, modelling fitting and appurtenance requires you to create a `.content` file, which you use [`PublishPartContent`](https://www.autodesk.com/support/technical/article/caas/sfdcarticles/sfdcarticles/How-to-use-PUBLISHPARTCONTENT-and-the-Autodesk-Aec-Content-CatalogEditor-exe-tool-to-add-items-to-the-Pressure-Network-Catalog.html) to create. It is quite a complicated process and requires you to create correct 3D solid model in AutoCAD prior to all this. Different fitting size may require you to draw different 3D solid model in different DWG file due to the intricacy of the connections. This complexity is not seen in pipes or even gravity structure. [![](https://civilwhiz.com/wp-content/uploads/2025/02/someoneme.jpg)](https://civilwhiz.com/author/civilwhiz/)[Ngu Soon Hui](https://civilwhiz.com/author/civilwhiz/) My passion is in [sharing knowledge](/about/) — Civil 3D or otherwise– with the world. I’m also the [benevolent dictator for life](https://mes100.com/about-ngu-soon-hui/) at MES Innovation Sdn Bhd.