I got a 3" x 3" upright 11 gauge steel short squat rack from a local equipment maker here in Atlanta. (Lynx Barbell) They do not offer spotter arms for the rack, so I searched far and wide to find a quality pair that would not only fit but was fairly priced and not branded. These arms fit great and provide the safety and variance that I was looking for to complete the centerpiece of my garage setup.
Got these to go with my Mammoth rack and they're exactly what you'd hope. They fit snuggly so there's no wobble and of course, they provide the safety that you need. I also use mine for rack pulls and functional isos, so the UHWM plastic liner is great to avoid metal-on-metal contact between the barbell and the rack.