4 Ruthenium

Re: Dell Inspiron 5577 2.5" Sata drive bay size. 7mm or

The drive needs to be 2.5" 7 mm or slimmer.  You also need a cable, bracket and screws (these will need to be ordered from Dell Spare Parts).

You can easily find a 1T drive brand-new (not refurbished) for around or less  than the cost of that refurbished drive -- shop around.