Hmmm ... although I have heard some may have had shear pins, I think most of the WH6s/Mk6s had a hubbed style prop, as opposed to the shear pin. Do you have a picture of your prop shaft that you can post so we can figure out what you are dealing with?
I am pretty sure that it is a sheer pin, atleast I think it is. On mine there is the propeller shaft with a pin running perpendicular to the shaft that the prop slides over. The best I can tell this "pin" makes the propeller spin. I think that I found a pin that I can use but I am just worried because the pin I found is made of a stronger metal than the old one.
They are made of various materials ... brass, stainless steel, bronze to name a few. A steel "drive pin" is used with a hubbed prop, as the hub is what slips to protect the gears.
JP
That seems to be the most common with the smaller HP (I think most of my motors have brass, too). If you want something that will shear a little bit easier, you may want to stick with it, as if your new one is steel, it will be quite a bit stronger.
East Coast sells sheer pins, I just don't know which one will fit yours since my WH6 was hubbed.