This probably also applies to other laptops made by Dell and to laptops made by other manufacturers. I won a Used Dell Latitude E6410 in an eBay auction. It had a 160 GB HDD (Hard Disk Drive) installed in it when I received it. I also purchased a larger Hard Disk Drive, a Seagate Laptop Thin 500GB 7200RPM SATA 32MB 2.5″ Hard Disk Drive (ST500LM021) from an eBay Seller.
Probably the 160 GB Seagate HDD I removed from the Caddy was a 9.5 mm drive.
In the case of my Dell Latitude E6410, the normal way to install a HDD is to turn the laptop off, turn it over, remove the battery, remove the Caddy with the old HDD, remove the Caddy from the old HDD, put the Caddy onto the new HDD, and then slide the Caddy and HDD back into the laptop and secure the HDD with the 2 screws. Then, install the battery and turn it over so the keyboard is on top.
That did NOT work for me, and apparently has not worked for many other people who participate in the Dell Customer Forum. It has to do with the SIZE of the drive (this is also true of SSD drives apparently) AND GRAVITY… The solution, after removing the battery and the old HDD, which I found on the Dell Customer Forum, is to install the new HDD or SSD (7mm) while the laptop is in the normal operating position (keyboard on top). Then, after the Caddy is installed, turn the laptop over again, install the 2 screws to secure the drive, and install the battery again.
This has to do with the position of the SATA connector in the Dell Latitude E6410 laptop and the size of the 7 mm drives.