Hi, I recently acquired four Tunze 6105's. It clearly states 6105 on the motors. Two have a blue, fixed propeller, with no shaft coming out of the front of the propeller. The other two have a black, moveable propeller, with a shaft that sits in the motor, and protrudes through the front of the propeller, into the front housing. So, the question is, What's the difference? Older vs newer model? which one would be the newest version and why?