I have a 500GB hard drive (model - HM500JJ) and I need to take the top cover off as I need to fix it but I can't seem to find the right screw driver for it. I've bought a Torx T8 screw driver and it seemed to have the right structure but it was too big to fit in and I've looked everywhere for a way to open it but just can't find the right screwdriver online.
Picture of female Line screw head from Wikipedia overlayed in red on your screenshot:
Looks more like a female Line screw head to me, not that I know anything about screws. According to Wikipedia Japan likes to use them on IBM computers, and Nintendo consoles. Samsung is Korean, but point being some tech companies do use Line screw heads. I'm not sure what size you'd need, but there are only 5 sizes (ALR2, ALR3, ALR4, ALR5, ALR6), and you can get 5pc sets.
My 1TB Samsung hard drive took a T6 Torx.
The screws on the 1 TB drive look to be the same size as the ones in your picture of the 500GB drive using the images on your drive sticker and the 1TB drive sticker for comparison.
I got a Kobalt 18-in-1 screwdriver set that had a T4, T5, T6, T7, T8, T9 and T15 along with some Phillips and straights for $6 at a local home center.
