This is probably an overhang alignment tool. If it is, it probably has a grid imprinted on it with an indication (either a hole or a cross hair indication for you to punch a hole)for slipping over the spindle. My suggestion is that you put a piece of tape or 2 to imobilize the turntable platter before you start. Once the tool is on the spindle, move your tonearm with cartridge attached so that the sylus gently rests on some indication..either an x or a dot which has been printed on the tool. If it cant reach this dot, or is too far forward of this dot, loosten the screws that secure the cartridge to the arm, and move the cartridge along the slotted holes of the arm so that the stylus sits right on the x or dot. You also must be sure that the cartridge is square within the indicated lines. Sometimes the arm itself may not be square to these lines, but your concern is the cartridge. If there is no slots in the headshell to accomplish this, the whole arm has to be moved - this adjustment is very important for good sound. Sei gazundt
