Divide 96" by five and you get 19-3/16" which is actually where the diamonds are located. It's just another layout setting like 16" or 24" commonly used for framing buildings.

They're for engineered trusses..........

Engineered trusses are a common usage but not the exclusive use. I'm remodeling an eighty year old house now for a customer. It was balloon framed with all members @19-3/16"oc My own house is log with the upper floor joists (4x8 timbers) @the same layout. It is more common in commercial work but not at all uncommon in residential.

thanks to all who replied.