Prop for older motor guide?

[frabillfisher]

I was wondering were i would go about finding a new prop for my probably 85 to 1990(not sure) motor guide trolling motor i know fleet farm carrys minnkota but not shure..only have one fin left on mine(got a little shallow on the river while bowfishing) and vibrates like mad when i use it

[frabillfisher]

WEll I think i might have found one that will work but im not sure when they say the diamiter i think or when they list a measurement about the blade what part does that mean like they say a 3 and a half inch..the opener is here dump