Split Fitting
To insert a split fitting, go to
Ribbon: 
Split Fitting
Pulldown Menu:
You will be prompted to specify the duct on which a split fitting is to be inserted.
Select duct or label to insert fitting at:
The Split Fitting Radius dialog box will appear.
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 🔘 Square Elbow with Turning Vanes Select this option to insert square elbows in the fitting with turning vanes included in them. Turning vanes will only be shown if the ductwork is rectangular.
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 🔘 Square Elbow without Turning Vanes Select this option to insert square elbows in the fitting without turning vanes included in them.
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 🔘 Radius Elbow: Select this option to insert radius elbows in the fitting. Specify the radius multiplier for the fitting. This value will be multiplied by the width of the duct to determine the radius of the fitting.
Select the elbow type for the fitting and press the button. A split fitting with the specified type of elbows will be inserted on the drawing, as shown below.
If you're having trouble inserting the split fitting, make sure the centerlines after the split resemble those in the image below. The duct that is parallel to the previous duct should be offset to favor that side of the split.
Radius for elbows: Sets the default value for the 🔘 Radius Elbow field.