Placeholder parts are 1-line dimensionless parts used for preliminary designs. When you draw systems with placeholder parts, the software inserts segments and fittings at appropriate points like other pipe types. You can convert placeholder parts to any other part type, such as commercial steel or copper tubing.
To draw a system with placeholder parts, configure a routing preference using placeholder parts in the default part catalog. The default Aecb Model drawing template includes a placeholder routing preference. Draw systems just as you would for any other pipe type. To convert the placeholder parts to other parts, modify the part subtype as explained in To Modify the Routing Preference and Nominal Size and To Modify a Pipe Fitting.