Volvo DuoProp sets have a 2 character designaton. First is an Alpha like A,B,C,D,F which indicates aluminum or stainless for a particular type of drive. The second character is a number from 1 to 8 indicating relative pitch. The higher the number the higher the pitch. Each step is 200-300 rpm difference. So, in your case for example, if you have a B7 then you want a B6 set to raise top RPM's relatively speaking. The number is stamped on the outside of hub between blades in one spot, and also on the inside around the splines.
A is Aluminum for 280DP.290DP, DPA-C for diesel engines. Thicker blades plus the rear prop is 4 blades.
B Is aluminum for same seris as the A but for gasoline engines.
C is Stainless for that same series.
D is Aluminum for later DPS style.
F is Stainless for that series.
E is for the Stainless higher performance DPX drives.
Not sure if this will work now, it used to upload ok before the forum upgrade...
Volvo 2005-2006 Prop Guide
View attachment Volvo_Prop_guide_2005_2006.pdf
