I received the shipment today, combined the sets, and have found there is a serious problem with the consistency of the size of the balls.  visually they look ok, but when you try to make a sheet from them, the sheet is lumpy and has ridges and valleys all over it.  this isn't a small problem of a few bad balls. (I have received one or two defects in other sets in the past)  This looks more like a big quality control problem witht the ball sizes, I can't just remove the bad ones, there are too many that vary too far in size, I can't easily identify specific balls that are worse than others because they all seem to be a slightly different size.

I've bought sets of 5mm balls from many sources in the past, in sets of 216 and 231, all but a few in nickel. (many of them were in the same packaging you sent, the metal cans with the foam liner)  Two sets I bought recently were silver and were 4.8mm, but were ALL consistently 4.8mm and work well with themselves, I just can't mix them with my 5mm sets. (of which I have ~25)  But the sets I got from you I can't even use by themselves because of the huge variety of sizing.  It's difficult to get an accurate measurement of a single ball, but based on what I saw when a few 4.8 got mixed in with all my 5.0, I would estimate these all vary randomly between 4.8 and 5.2mm, which is more than enough to disrupt the geometric shapes I am trying to build with them.

If you would like to test some of your sets, take out 4 or 5 and make a single string.  wrap 6 balls around 1.  continue to wrap in a spiral, with 12 around the 6, and so on until you use all the balls.  set it down on a flat table.  feel how lumpy it is!  If you press down and flatten a lump, something else pops up!  When I do that with any of my other sets (30 of them) I get a smooth flat sheet with NO lumps.  If you try to make large geometric shapes with inconsisten ball sizes, things won't line up and the shapes won't fit or hold together properly or will collapse.  Even a single bad ball can cause problems.  Of all my older sets, I had to remove 3 balls in total that were defective (too large or too small)  That's not too much, 3 bad out of 7000.  But these new ones are TOTALLY inconsistent, I can't remove the bad ones because there's no one majority "good" size.

I don't know how to handle this.  If it were only one or two sets I would just take my lumps and use them for smaller things, but this is 40 sets, I spent a lot of money and am not willing to just write it off.