Dell wanted to charge me $20.99 on this plastic caddy, so that I could install a 2nd backup hard drive to my newly purchased DELL computer.  (I purchased the new hard drive on sale at Best Buy.)  Every computer I have ever owned allowed for a 2nd hard drive to be screwed into the tower easily, EXCEPT this one.  This part works perfectly in the Dell Optiplex 3010 and substitutes for part number KK4N0 (which is what they said I needed to buy).The new computer has been working fine, except for a glitch with the loose connector on the power supply.  They sent 2 power cables before sending a new power supply. For all the hassle though, they could not send this plastic part for me to install a commonly added backup hard drive to my new computer.Note- I did need to buy separately the 90 degree SATA cable to add this hard drive to the system.  (Also bought at Amazon.) Great service on that too!Anyway, problem solved!  This part also arrived more than a week before the estimated delivery time.  Very FAST service and well packaged.  Thanks!!!!!!!!!