8/16 to 9/16 pitch (thin blade), your cone size and reduction nozzle size will make a difference.
Sometimes the prop isn't exactly the same pitch, so a pitch gauge is handy to give you a base point. Each prop seems to be different so it's hard to just pick a number. They always seem to read higher when I look at them. I wonder if the number is the measurement between the blades when it's a lower pitch?
Ashby Griffith (Jett Lab Products) has a nice affordable pitch gauge, other options are available too.