Thru-hub exhaust propellers are used on most outboard & stern drive engines. You have a thru-hub exhaust if there are exhaust holes on the engine gearcase around the shaft.
Thru-hub boat props consist of a round barrel (the hub) to which the blades are attached.
The exhaust passes through the barrel and out the back, without making contact with the propeller blades.
This provides a good clean water flow to the blades, usually resulting in good acceleration and hole shot.
Non thru-hub exhaust systems are found mostly on low horse power outboard and stern drive motors, and where inboard ski props are used.
You have a non thru-hub exhaust if there are NO exhaust holes on the engine gearcase around the shaft.
Over-hub exhaust propellers have the blades attached directly to the smaller tube that fits over the propeller shaft, eliminating the larger exhaust tube.
These types are often used for attaining maximum top speeds.
On some vessels, the hole shot can often suffer due to the extreme exhaust flooding that occurs around the blades during acceleration.
Over/Thru-hub exhaust propellers are a combination of thru-hub and over-hub exhaust.
This allows some exhaust to escape at lower RPMS, providing a controlled amount of exhaust flooding.
These types will allow the propeller to be slightly easier to turn during initial acceleration, allowing for a better hole shot on some engine/boat combinations.