Be careful when upgrading from a Seagate drive
This is not so much a question as a word of caution for other potential upgraders. I pulled my Apple 'coffee can' A1470 apart to find the 2Tb Seagate as others have described.
I purchased a 4Tb RED Western Digital (WD) to replace it. When inserting the drive back into the drive space I noticed a difficulty in getting the rubber moldings in the bottom of where the drive goes to wrap around the new drive. Upon closer inspection I discovered that the old 2Tb Seagate has a slightly larger cutaway on the metal folding of the metal case of the drive. To get the WD to fit I had to take a really sharp thin blade and carefully slice away to make a bigger space for the bottom of the WD drive, on both sides, with both rubber moldings. Having done that the WD fitted back into the chamber quite OK. I would also add that the small wire connections I had to take off and then refit are the smallest ones I have ever come across. I needed a torch and a small pair of tweezers/forcips to be able to get them back in place. Overall, definitely not a job for anybody who might have been called 'Kaptain Klutz' in the past. The new drive works well, and possibly I may be tempted to upgrade to a 6Tb next time.