Black Brant 2B
Actually there were only a few Black Brant 2 Vehicles that had 3 fins.
Most of the Black Brant 2 Vehicles had 4 fins
There were several versions of fins used on the Black Brant 2 vehicles
In case you were wondering what one looks like , Here is a photo of a Black Brant 2 Igniter
The white tube is filled with small chunks of propellant .
The igniter screws into the top of the motor and injects a flame down the middle of the motor core
This type of igniter was also used on other Black Brant rockets