From the Conn catalogue,
"The Model 78H 'Artist Symphony'
First chair symphony trombonists have especially preferred this fine model. With it's 8" brass bell and .522" cylindrical bore dimension, the 78H produces a rich, dark tone though somewhat lighter than the 8H and 88H. Include nickel-silver out tuning slide, nickel silver joint reinforcing rings, nickel silver chrome plated inner slide, P - 27 special allow [for increase durability] out slide."