To secure your new drive in your iMac, you will need to place high strength double-sided tape at the four corners on the side of the drive with the SATA connectors.

Peel the backing off one side of the double sided tape.

Press the exposed adhesive side of the double sided tape to the corner of the SSD.

Be sure not to cover the SATA connectors with the double sided tape.

Repeat the above process for the remaining 3 corners.