You can find information on your existing motor label that will help you in selecting the correct  replacement.  Some important information to find is the frame, RPM, amperage, horse power, shaft (threaded or keyed), single or three phase, and if your motor is a square flange or a C faced motor. 

To determine if you have a Full Rate or an Up Rate motor you will first need to find the motor's service factor (S.F). This number along with the motor's horsepower, can be found by searching the motor's label. Once the service factor is located, use the chart below to determine the rate of your motor.