How to open the external hard drive case.

Hi, Most Seagates HDs uses Torx (type of screw head characterized by a 6-point star-shaped pattern). TORX sizes are using letter "T", followed by a number. A smaller number corresponds to a smaller point-to-point dimension of the screw head. These are also used by cellphones but smaller sizes. Normally you can buy a plastic box set containing 6 Torx drivers of varying sizes, hopefully one will fit you HD. However, if you are referring to the enclosure of the actual HD, they might or might not be using the same kind of screw. Hope this be of help/idea. Post back should you need further information. Good luck and kind regards.