Radius v. Diameter for MEP Connectors

When placing round connectors in families, Revit allows you drive the dimension of the connector with either the diameter or the radius, but there is a catch.

All of the round connectors must be driven the same way. 

When editing an existing HVAC family to add some hydronic connections, I couldn't change from diameter to radius. A quick test revealed that the round duct connector already set to diameter was locking all round connections to diameter. I deleted the duct connector and the radius choice reappeared.

In this case "all or nothing" set to radius was not a problem, it actually cleaned up the family. It just just a quirk that good to know about.