In this chapter we looked at the three critical specifications of a high pressure pump: horsepower, pressure and water output. We reviewed how to figure out what size orifice to use based upon these pump specifications and how many cutting heads are being used. We covered the productivity increases and cost savings of using two smaller orifices versus one large orifice. Additionally, abrasive nozzle diameter selection was discussed in terms of the ratio to the orifice being used. Finally, we looked at waterjet feed rate calculators and how Machinability Indices can be used to extrapolate the cutting speed of one material from a different material.