I don't know how anyone can squat with a 45lbs bar. Personally, I only back squat with my TSB and it's 55lbs. I tried using a TPB in a pinch b/c of time and it felt like a toothpick. Couldn't do it. I use a 45 for my front squats but never back squats.
The 52 lb bar mentioned above is 32MM diameter. Not bad.