Hi Coast Guard,
If the picture below is representative of your Dell Precision 3620, you will need a 5.25" to 3.5" adapter to fit the Graugear panel into your computer.
Many years ago, most PCs came with a 3.5"floppy disk drive and (optionally) a 5.25" CDROM or DVD optical drive, so most computer cases came with a number of 3.5" and 5.25" bays.
Floppy disk drives disappeared from common usage at least 10 years ago, but manufacturers continued to use the empty 3.5" bays for fan speed controllers, USB ports and card readers. More recently, case manufacturers stopped fitting 3.5" bays and many cases do not include 5.25" bays either, but fit fans from top to bottom.
Your computer only comes with a couple of 5.25" bays, so you will need an adapter to make the 3.5" Graugear panel fit.
The Startech unit below will allow you to mount a 3.5in panel in a 5.25in computer bay.
https://www.startech.com/en-us/search?search_term=3.5 to 5.25 bay adapter bracket
Before buying anything, remove the side panel of your computer and seach for empty USB3 ports on the motherboard. If you don't have any free ports, you cannot use the Graugear adapter.
In order to make use of the SD card reader on the Graugear panel, you MUST have a 19-way header like the one below. This port is fitted on most modern motherboards from MSI, Gigabyte, Asus, Asrock, etc., but I have no idea if Dell include it on theirs. Quite often the colour of this header is blue, but in the second image below, the 19-way connector marked USB3.0 is black.
If you want to make use of the USB-C connectors on the Graugear panel, you will also need the connector outlined in red in the image below. These ports are less common, but are fitted to many mid-range and high-end motherboards. Again, Dell may not have bothered to fit this feature on your PC. N.B. The Gen2 port is quite small, approx 12mm (1/2in) long. It's easy to miss if hidden by cables.
If you don't have either of these USB3 ports on your Dell motherboard, don't waste your money on the Graugear or any similar adapter. Instead, you'll have to use an external SD card reader.
Quality external USB3 readers from Kingston and Lexar are reliable and easy to use. They are also cheaper than the Graugear panel + 5.25in to 3.5in adapter.
If you are tempted to buy a $5 multi-card USB3 card reader, don't be surprised if it fails to work reliably.