I can't say what nipples your gun needs except to say it will be the short pistol nipples, not the long, rifle nipples.
The reason I can't say is your gun could have been built by Uberti, Palmetto, Pedersoli, Pietta, Armi San Paolo or a half a dozen other companies.
Although these companies did use different nipple threads, most of the other parts that might need replacing are so similar that they will either drop in place or need just a little modifying to make them work. The cylinder might be the exception to this.
The nipple threads are probably metric. Metric threads are becoming common enough that most hardware stores and auto parts stores have them and the tools needed to measure them.
Take one of your pistols nipples to one of those stores and ask them to tell you what the threads are.
They are probably 6mm X 0.75mm threads.
A few companies might have used the American #12-28 thread size but its unlikely.