Xbox 360 Slim HDD must

Empty shell (Enclosure) for 2.5 "SATA hard drives for Xbox 360 Slim.
Ideal for those who want to expand the memory of your Xbox360 on their own or for those who plan to use a larger disk on an Xbox 360 with JTAG.

Think about this:
The hard drive must not be higher than 9.5mm, double check this if you are going to have 750GB or more in capacity as these are often a bit higher.
If you need to use your own hard drive for your 360, it must be formatted correctly with the right security sectors.
Microsoft has only officially released 250GB disks and therefore you cannot get more space on your own hard drive you put in the cabinet itself. On the other hand, if you are running an Xbox 360 that has RGH / JTAG, it shines bluntly in these security sectors. In the latter, you will not be able to move your disk to another 360 as long as it is not specially chopped it with.

Note that the image on the product may differ marginally against the product being delivered.