To decide what top sub you need will depend on what you are going to attach it to. If it is going to a sonde housing, you will have a box end on your sonde so the motor should have a pin end with the same connection as your sub. If it is going to a monel drill collar, then a crossover sub might be used and this might be one you have in stock. The top sub should match those connections. Adtech can change top subs on most motors to satisfy the need of most drill string. This should be discussed with Adtech Sales. Adtech can provide crossovers as we manufacture them on site.