The maximum reach of the blade from the center of the propeller hub. It separates the leading edge from the trailing edge. (UP)

B. Leading Edge

That part of the blade nearest the boat, which first cuts through the water. It extends from the hub to the tip. (UP)

C. Trailing Edge

That part of the blade farthest from the boat. The edge from which the water leaves the blade. It extends from the tip to the hub (near the diffuser ring on through-hub exhaust propellers). (UP)

D. Cup

A small curve or lip on the trailing edge of the blade, permitting the propeller to hold water better and normally adding about a ˝" (12.7 mm) of pitch. (UP)

E. Blade Face

That side of the blade facing away from the boat, known as the positive pressure side of the blade. (UP)

F. Blade Back

The side of the blade facing the boat, known as the negative pressure (or suction) side of the blade. (UP)

G. Blade Root

The point in which the blade attaches to the hub. (UP)

H. Inner Hub

This contains the shock absorbing hub (described below). The forward end of the inner hub is the metal surface which generally transmits the propeller thrust through the forward thrust hub to the propeller shaft and in turn, eventually to the boat. (UP)

For through-hub exhaust propellers. The exterior surface is in direct contact with the water. The blades are attached to the exterior surface. Its inner surface is in contact with the exhaust passage and with the ribs which attach the outer hub to the inner hub. (UP)

J. Ribs

For through-hub exhaust propellers. The connections between the inner and outer hub. There are usually three ribs, occasionally two, four, or five. The ribs are usually either parallel to the propeller shaft ("straight"), or parallel to the blades ("helical"). (UP)

K. Flo-Torq™

Shock-Absorbing Rubber Hub Rubber molded to an inner splined hub to protect the propeller drive system from impact damage and to flex when shifting the engine, to relieve the normal shift shock that occurs between the gear and clutch mechanism. (UP)

L. Diffuser Ring

Aids in reducing exhaust back pressure and in preventing exhaust gas from feeding back into propeller blades. (UP)

M. Exhaust Passage

For through-hub exhaust propellers. The hollow area between the inner hub and the outer hub through which engine exhaust gases are discharged into the water. In some sterndrive installations using a through-transom exhaust system, this passage carries air. (UP)