Hello. You seem correct. All the information I have looked up indicates that the DVD, SATA  Assembly is of the  height 12.7 mm and not 9.5 mm. I am going to bring this discrepancy to the attention of a concerned team to have the user manuals corrected. Thank you
Seemed like a no-brainer to install an optical drive in my new PowerEdge T20 but, no. The manual says: NOTE: Only slim 9.5 mm SATA DVD-ROM drive or DVD+/-RW drive can be installed in your system. External optical drives can be connected through USB ports. Trouble is, the manual's wrong, I think. A 9.5mm high drive is too small (not tall enough). Or am I missing something totally obvious? TIA  Bob Crabtree 
PowerEdge T20 manual says to use a 9.5mm (slim) optical drive but it's too small