I thought the same thing when I got mine. The mounting flanges will bend outwards toward the sides of the bucket quite easily when you snug it down and remain in that position. You'll only have a bit of a struggle mounting it the first time...BTDT
EDIT: If I recall correctly, I cut a 2x4 to fit inside the width of the bucket in order to brace the sidewalls of the bucket when installing the piranha bar. That kept the sidewalls of the bucket from deforming which caused the mounting flanges of the tooth bar to bend out flush to the bucket.
Edit/Edit: Never mind, I just saw that you already installed yours.
I didn't see any deformation in the bucket, and what I read on the site, the mounts are supposed to flex out to the sides. They're pretty thick, and it's gonna take a LOT of force to bend them. I don't have a clamp (that I can tighten enough) to pull those out without the bolts in them. I tightened the bolts with an electric impact that I've had since about 1979. I've wrung off 1/2" bolts with it, so I know it'll get 'em tight. With them as tight as I dared put them on with that impact, there's still nearly 3 threads showing inside the nut. 2 threads is supposed to be enough to hold the shear strength of the bolt, but I've never been one to trust or test that theory. I like seeing at least a couple threads of the bolt sticking out of the nut. I thought they were 1/2" bolts, but they're actually 5/8".
My bucket has a small tear-drop shaped reinforcement in the corners, which adds 1/4" thickness to each side. My guess is to keep from ripping the side panels out of the bucket. I'm wondering if BXPanded compensated for that thinking I'd measured to the side panels of the bucket, despite their instructions to measure the narrowest distance at the bucket edge. They also asked for the total length of the cutting edge. The bar is about an inch shorter on each end (2" shorter, total). Not a problem, just an observation. The bar length matches the inside width of the bucket. Not sure having anything sticking out past the bucket sidewall is useful. I'm pretty sure that I'm not the first customer with my bucket model number, so they've probably tweaked their design a time or two for measurement errors.
It sliced through the first root I hit with it like hot butter. With the bevel of the cutting edge turned up, it'll peel anything out of it's way, between teeth or on the ends. Smaller roots would stop the factory edge from digging at all. I keep saying, I'm very happy with the product, but the packaging could be improved. Were it good packaging to start with, this post never woulda happened, which in a way, would actually be a bad thing. Not that the damage not happening would be bad, but that thorough review of part of the quality of a purchase would not have been discussed. Perhaps if a survey is permitted, it would be more useful to collect data on who has the Piranha, and was the box destroyed when received. Would be interesting to see how many received it with pristine boxes.
Most of us grownups are excited to see our new toys and seldom look at the packaging. At Christmas time, kids take the gift out, throw it down, and go play with the box, especially toddlers. I guess that's the difference in living long enough to judge a box based on what it's intended for.