Prop Exhaust Types

Thru-hub has holes around the prop hub.

Thru-hub Exhaust

Most outboard & stern drive engines vent exhaust thru the prop hub.

You have a thru-hub exhaust if there are exhaust holes on the engine gearcase around the prop shaft.
Non thru-hub is solid around the prop hub.

Non Thru-hub Exhaust

Non thru-hub exhaust systems are found mostly on low horsepower motors.

You have a non thru-hub exhaust if there are NO exhaust holes on the engine gearcase around the prop shaft.

Prop Splines

Spline Example Count the teeth on your prop shaft to determine spline count.

Prop splines are the little teeth you see on your prop shaft and inside the prop hub.

The number of splines on the shaft and inside the prop must match for the prop to fit your boat.

A Pin Drive prop application has no splines. The prop is secured to a smooth prop shaft with a pin through the shaft.

Propeller Rotation

Props spin either clockwise (standard or right-hand rotation) or counter-clockwise (counter or left-hand rotation).

Most single engines use a standard rotation prop. Most twin engines use one of each.

To determine what prop rotation you have, look at your prop as if on a boat. Position a blade pointing straight up. If the right-hand side of the blade is closer to the boat than to you, it's a standard rotation prop.

Mercury Marine Black Max Boat Propeller:
  • Manufacturer: Mercury Marine
  • Prop Family: Black Max
  • Part Number: #48-77342A33
  • Rotation: Standard Rotation
  • Diameter: ?
  • Pitch: ?
Mercury Marine Black Max Propellers
Prop Exhaust Types Prop Splines
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Propeller Help Guide