We have designed our transitions from one inner diameter to another using a special S-Curve. This feature strengthens the part, as does our guarantee of machine work FREE OF TOOL MARKS AND CHATTER, critical in a safety part such as this, where a stress riser could propagate a crack under the stress of vibration and torque reversal. Because imbalance can have catastrophic results, we also guarantee PARALLELISM between the faces of the prop extension, as well as CONCENTRICITY among centering boss, center bore, barrel OD, flange OD's, and bolt centering.
For engines over 150 hp (0320, 0360, etc.) that use wood or composite props, we offer extensions with a 7" diameter prop flange, thus providing more than a 30% INCREASE IN GRIP AREA, while adding only 5 ounces of weight. Wood props are subject to the effects of changing temperature and humidity, and the added grip area greatly decreases the prop's susceptibility to loosening.
Our threaded lugs are machined from 17-4 PH STAINLESS STEEL, flanged, and held to the close tolerance required by their interference fit. Unlike tubular lugs which can vibrate forward into the counterbores of the wood prop, our lugs are custom machined with a shoulder to prevent such forward movement. Internal threading allows the removal of prop or retorquing of bolts with the upper cowling in place. Our choice of 17-4 results in a THREAD OF SUPERIOR STRENGTH over 4130 alloy steel, while preserving the same characteristics of ductility, lack of brittleness, and freedom from galling. The 17-4 also offers excellent corrosion resistance, which is a weakness of Cad plated alloy steels.