The drill bit size is selected by the customary size for the largest OD of your drilling string, including the drilling motor. Since the drilling motor is probably has the largest OD, then this will be the size Adtech will use in recommending a drill bit size. Our Recommendations page will give you the sizes that normally run with Adtech motors. The type of drill bit is decided by the formation you will be drilling in. Read about what bits are preferred in specific applications in our Drill Bits 101 guide.