If you have a lot of DIMMs to send in I strongly recommend considering the USPS Priority Mail Flat Rate Medium Box. 7 rows of gold fingered DIMMs, standing on end, fit perfectly in the box as you can see in my attached photos. (There's just shy of 23 lbs of RAM in the box in the photo.) Once the box is closed there's almost no room for the RAM to shift around. It's almost like someone designed this box for shipping DIMMs.

I'm wrapping the entire box in a heavy duty fiber reinforced shipping/strapping tape. There's no way it would survive a trip intact using regular old light weight packing tape.

Bingo.

I use Duck or Scotch strapping tape

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42 6F 61 72 64 73 6F 72 74 2E 63 6F 6D

That's a pretty good deal! I sent in a medium box recently with 5lbs of ram and 5lbs of processors.