Take time to carefully slide hard drive while pulling out on the sides of carrier for expanding its width to accomodate the pins on the sides of the carrier which are inserted into the holes on the sides of the drive. At first it may seem impossible but installation is certain with perseverance and careful insertion. I guess I tend to be cautious because I was concerned about potential breakage of the plastic guides on the carrier. It's a tight fit but it is designed that way. I am very pleased with the simplicity of the design and that this fits so well considering its part number may not match the one itemized in the HP parts Surfer site when entering the serial number of the Z620 Workstation. I am very happy with this product.