the 13 1/4 is the diameter of the prop, the 19 is the pitch, 1/4 " will be minimal performance wise compared to the pitch increase. It just means that you'll have a touch more clearance under the AV plate. Sometimes you need to drop a shade in diameter to accomodate the extra pitch anyway, that might be why it's a 13 & not 13 1/4.
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5