Since steam engines are slow speed and have a lot of torque, you need a prop that has a pitch equal to the diameter ie: 1.75" diameter with a 1.75" pitch. Propshop has a whole list of props available. If you don't see exactly what you need in how they are set up for your shaft, give them a call. They will drill or tap a prop to whatever you need. They have done it for me several times.