Mount new, carry a spare.
Read the chart and know what the markers mean.
The marker system may not be familiar to you and I think that is how much of boat damage is done here.
An SS prop has different performance characteristics than aluminum. It's not just about corrosion and salt water.
Also, an SS prop hitting a rock may transmit more of the impact to your prop shaft and vertical drive shaft than an aluminum prop would.
It can transmit more impact to your wallet as well.
