I used 5/8"for the current box I'm running now.. it pulls 145s unbraced.. my car flexes more than the box lol ..
5/8" is only an 1/8" inch smaller than 3/4".. that is not much of a difference. but if its for competition brace if like chad said.. you could get away daily without bracing, that is unless your running a lot of power with some crazy subs. what are you going to be running btw?
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