Total 5 partsOnce assembled, they are already assembled for delivery, so you can simply replace the batteries after assembly.(Test batteries are included, but may not be used in the event of a natural discharge during delivery.The coin battery has a flat side on the sensor side. Please note that some rod can be casted, but casts in a full swing may result in a centrifugal force.How about taping it to prevent it from flying? Ask for information.