PC Case Kit – GPU Trim Modification
The right-hand graphics card in this image can slide into the slot provided on the back panel of the case, so can be fitted without any modification. The one on the left however has a prong sticking out, which prevents it from fitting properly.
So to fix this, first use a pair of pliers to grab the tab as far in as possible, and then bend it first one way...
If necessary a file can also be used to trim it down further.