Well due to an accident I have a bent and cracked prop and need to replace.
The accident involved my wife moving the boat around the driveway without a
vehicle and without tilting the motor up, she lifted the hitch end of the
trailer up too high and the back end of the boat slammed the pavement.

I was told by the previous owner to keep a few spare "shear pins" handy in
the boat in case of a prop strike on the water. Apparently these pins are
supposed to break instead of the prop in this situation. Well tonight I
removed the prop to take with me to the boat store for a replacement and I
just can't see how this thing would work. What I see is the first 2 inches
or so of the shaft is threaded followed by 7 or 8 inches of straight slots.
The prop is groved to fit the shaft slots and there is a washer after the
prop also grooved to fit the slots. A lock nut then fits on the threads and
a pin is placed through a hole in the shaft and grooves in the nut to
prevent the nut from working itself loose. I am assuming this is the shear
pin.

It seems to me the only thing this pin does is secure the nut from slipping
off the end of the shaft. Is it just me or is the idea that this pin will
break and save a prop false? I really don't see how this would work since
the nut is well threaded on to the shaft (at least an inch) and the shaft is
slotted to fit grooves in the prop. I can't see this pin breaking, the nut
slipping off, and the prop sliding off the grooves fast enough to prevent
damage to the prop, shaft, lower unit and other parts of the motor. Is there
something here I'm not seeing? Have I mistaken this pin for the shear pin?