For my DIY ground wires, I used a couple of approaches. Most of my DIY ground wires were fashioned from ersatz (?) Chinese Nordost green filament-wrapped clear insulated 16 gauge solid core silver plated copper wire sourced online from Aliexpress. For the Ground Block end I simply doubled the wire back tightly on itself which then fits firmly into the Block and looks cool in a bachelor pad sort of way. I added heat shrink tubing to each end help dress and support the ends. For others I used 2mm bananas like those cited by Dave above.
Andy
Andy