HP Work Station require 3.5" Caddy, but you have 2.5" Hard Drive, So you need our this converter to change your 3.5" Caddy to 2.5" Caddy

Compatible Part Numbers:
HP Z820 Z840 Z620 Z640

Works with the following 3.5" HP drive trays:

Fit Model
HP Z820 Z840 Z620 Z640

Package Include
1*Converter
8*Screwer