Parametric Magnetic Separator Rack for 0.2mL tubes

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I was introduced to SPRI bead cleanup by Ethan Ford when doing NGS library preps, and it was a really easy way to clean up many small volumes of DNA quickly and easily. The protocol for homebrew beads that Ethan had made it a very cost-effective method to purify PCR fragments and elute them in tiny volumes that were problematic with columns I was using. Given I had leftover beads from my NGS preps, I set out to print myself a separator rack, which is essentially a magnet that costs hundreds of dollars. As a cheapskate, this rack isn't designed to fit typical 96-well plates or strip-tubes; instead, the spacing between tubes is designed to place them at the interface between cheap 5mm Neodymium magnets I found on eBay for ten cents each. This setup seems to concentrate the magnetic flux in those areas or something, but it makes the beads clump nice and tight in the tubes.