I have also studied this problem. When I was watching videos to learn, I encountered the video below.

This flange is generated using library features.

The library feature folder is generally placed under Design Library\Feature. The corresponding folder path is: C:\ProgramData\SOLIDWORKS\SOLIDWORKS 2016\design library\features. There are many library features in this folder that can be reused when designing parts, such as drilling, extrusion, scan removal and other operations.

The library feature customization process for the flange in the picture above is as follows:

Create a new SW part, do not do anything, perform the "Save As" operation, and select the file type when saving. "Lib Feat Part(*.sldlfp)" is the library feature file type. Save the file to the features folder of the design library, or create a new Flange folder to save it. You can choose the file name as needed.

After saving, use 3D sketch to draw a line passing through the origin, and then draw a straight line that is not parallel to the line, so that the end point of the second line coincides with the first line, and set these two lines is the construction line.

Use the endpoint of the first 3D straight line and itself to generate reference plane 1, and use two 3D straight lines to generate reference plane 2.

(Please note that reference plane 1 should not be generated using the origin. )

Draw a circle on reference surface 2 to generate a cylinder. This cylinder is equivalent to the equipment cylinder in the picture above.

Draw the flange and the short tube on the reference surface 1. When the short tube is stretched, select the shape to the specified surface. Select the cylindrical surface generated in step 4 for this surface.

Hold down the Ctrl key, select the features of reference surface 1, flange and short pipe in the design tree window, right-click and select "Add to Library". Do not select others, such as two 3d Line, cylinder from step 4.

After the above is completed, you can see that there are vertical arrows on the design tree species reference surface 1, flange and short pipe features, indicating that they have been added to the library successfully. Then hide the reference surface, reference line, cylinder generated in step 4, etc., and you can preview the flange we just built in the feature folder under the design library on the right. Then you can pull out the flange and use it when designing the equipment.

Of course, you can use the added design table to create flange library features of different specifications, so that when using it, you can select the corresponding specifications as needed like in the video.

The above is basically the modeling process of this flange library feature. However, if you want to use it well, there are many details. It is recommended to go online and watch the modeling learning video of the library feature.

When I first built this library feature, I directly used both ends of the first 3D line to generate reference surfaces. When the short tube was stretched, it was to the reference surface, which was used for the library features after it was built. At this time, it cannot be formed into the equipment cylinder. Later, I carefully studied the stretching of this short tube and found that the reference surface is plane and the cylindrical surface is face. The characteristics of the two surfaces are different.

This is the flange library feature built using the above method